This is a bit tricky to do and very risky if you're short on gold. In order to do this you will need to break apart a stack of items into small portions, either singles or doubles. Load a few of them onto the Auction House for a dirt cheap price, but still within a reasonable range. Say you are doing it with Embersilk take 3 or 4 singles/doubles and load them onto the Auction House for a low price. For singles I usually do 1g 20s each or doubles 1g 85s. Make sure not to load both singles and doubles on the AH at the same time for those prices because you will lose more money than you should since people can buy out the doubles without it affecting the singles.
Now, the reason for doing this is that when Auctioneer goes to undercut the Auction House it takes the lowest price and undercuts it, regardless. This will make it so anyone that blindly uses Auctioneer will undercut your already extremely low prices. If I need to spell it out for you, this means you will be getting massively good deals that YOU can control. Now like I mentioned before this is risky and easy to mess up if anyone buys out your low priced item. Usually people won't care about a single low priced item though, since it isn't worth their time to buy it.
There are a lot of variables that you need to keep in mind when trying to play this trick on people. One is don't low ball the Auction House to a point where someone is going to know you're up to something. Or to a point where someone is going to laugh and buy out the item you put up instantly for being dumb enough to put it up for such a low price. For example, putting up Embersilk for 1s is so unreasonable that it will be bought instantly by the first person that sees it and no one is seriously going to believe that Embersilk is going for 99s a stack when their Auctioneer goes to undercut. You have to be realistic when doing this, in the middle of "I can't believe it is so cheap..." and "Eh, I've sold it for less...."
As mentioned before, I know I can sell Embersilk Cloth for 29g each 100% of the time on my server, so I try and get people to put their stacks up from anywhere between 22g and 25g. Also as I will mention time and time again you only want to do this during the peak hours on your server, preferably only on the weekends. Since you are putting stuff up on the Auction House for so cheap you will lose money and there is a 99.99% chance your item will sell for that dirt cheap price by someone looking for a deal. The main idea of this is to buy out as many items you can that are undercutting yours for as long as possible before someone buys out your item.
That means if you do it on a weekend, during prime time the most people possible are online and you have the best chance of people Auctioning items which can undercut yours. Here are some pictures of me showing you how it is done and proof that it is working. Even though the first example isn't Embersilk, it is still in the cloth catagory and perfect proof it is working... Hell I didn't even have to do the work for this one!
Notice how this guy flooded the market with singles for much less than a stack should go for (I can sell a stack of Netherweave for 12g easily). Now he put a bunch of them up for 49s each, which is a price that is inbetween the two ranges that I told you about earlier. Notice how people just listened to their Auctioneer and started to undercut the price of his singles? Then they undercut the undercutters? (Gosh darn undercutting undercutters that are undercutting the undercutters!).
Since people are too lazy to buy out the singles they just sit there and are used as "bait" to catch people into undercutting them when they blindly listen to their Auctioneer. Anyone that doesn't check the Auction House before putting their Netherweave Cloth up will wind up undercutting the cheap single pieces of Netherweave which will make the stacks of Netherweave easy to buy and also extremely cheap. Here is a picture of some Embersilk Cloth "bait" on my server.
Once again I didn't even have to initiate this one, it happened all on it's own just like the Netherweave shown above. Now you can do one of two things when you see this, buy it all and turn a profit or leave it and hope to catch a bigger fish with a full stack undercutting the singles. I find it best to make this decision based on the time of day and what day it is. Right now it is 5 in the afternoon on a Friday so more people are playing then usual which means I am going to leave it on the Auction House and try to catch a bigger fish rather than buy it out and turn an extremely small profit on it.
Both of those two examples along with all of my explanation should be sufficient enough to teach you how to do this without having to actually do it myself and show you. For more information on this though, listen to and watch my videos.