Yeah, check out this link for the AutoReallyRun files:
http://www.gp32x.de/board/index.php?/topic/48812-autoreallyrun/
Basically, you download ARR and unzip the files to the root of your SD card. Make a backup of the autorun file that's already on the SD card (just in case), then run autoreallyrun_on. It'll tweak the autorun (while making a safe backup copy) so Gmenu will become the new frontend.
It isn't perfect; sometimes some programs will just kick you back to the default Wiz frontend no matter what. Also, some games don't run properly through Gmenu to begin with. If you wind up back at the default frontend, just find and run autoreallyrun_on or the gmenu2x.gpe to get back to Gmenu.
I've also noticed that Gmenu on the Wiz doesn't seem to let you do anything with a USB connection (other than charge), so if you need to connect it to your PC, run autoreallyrun_off to get back to the default Wiz frontend. When you run ARR_off, it restores the original autorun, so when you're done you'll need to run ARR_on again. It's a bit of a hassle if you need to do this regularly, but since I don't know anything about Linux programming, it seems to be the only option.
ALSO, the GP2x skins for Gmenu all seem to work just fine on the Wiz!