I found this a few weeks ago when Wrath launched and I was leveling my Alchemy up.
Screenshots before explanation:
http://i35.tinypic.com/2w36yb5.jpg
http://i37.tinypic.com/21msuf8.jpg
What you do is this: Get your random eternal that you intend on transmuting and mats for another combine of your choosing. The first screenshot I just randomly made what I had mats for, the second I made with intentions of using and figuring out if the first time was just a fluke. Anyways, get the mats for the other elixir/potion/whatever ready and click combine on your transmute. Midcast on the combine select the other Alchemy recipe you have materials for, and immediately after the transmute finishes click combine. The best I can tell is the discovery chance is transferred over to the recipe you selected midcast. I discovered all of the recipes in 3 days, a friend used the same method and it took two.
by brav