I'm not optimistic about this working on the Pre. I'm still using aliases from accounts I set up solely to use as a "reply to" accounts. Unfortunately, these accounts still sync even though they are set to manual. It would be nice to have the GMail alias feature work on the Pre, but at least it works on the web.
Additionally, I just realized that it won't let you have different account login settings for incoming and outgoing. I had set my outgoing to the server that I wanted to use, and it changed my incoming login settings to match those. Had to switch back.