I want to compile Qt without the mt (multi-threaded) flag. Is there an "in-system" way to do that, or do I have to cheat and build it by hand, touch compile and then emerge the KDE stuff? It would be nice to be able to pass configure flags on a per-package basis through emerge (or some other means).....
I dont remember if the qt ebuilds use eclasses or not (which makes things a little more complicated), but you should be able to add/remove configure options as you please in the ebuild, then just merge it as you normally would.
Keep in mind that when you do your next rsync, the ebuild will be overwritten with a fresh one from the server, so your modifications will be lost.