tremfusion client from tremfusion.net might help. I think it's a stand-alone [doesn't require default 1.1 to be installed and things like data-1.1.0.pk3] so i guess it should work.
It probably doesn't contain default maps though [i think] so you might want to move your maps into your user/libray/appsupport folder.
Like i said, i'm not sure since i havn't used a mac for so long.
As you said, you could get trem gpp/1.2 instead, but the gameplay is almost completely different such as the way you build bases [you can't just spam turrets in a U shape anymore for most cases]
