i think your question was answered above, but no, you cant directly mouse over bind a mouse button to the average frame, in so far as i know anyway, but then, why you would you want to or need to?
grid + clique is a defacto (also healbot and voodoo, although i rate the grid/clique setup as the best by far) mouse over macro add on for mouse buttons, the only difference is, instead of moving mouse all over your screen you move over grid and press a button. i realize that pressing a button is a little different, but honestly is pushing a button really that bad :P
Ive tried out mouse over, and i found it didn't really improve my game much and it felt like it was removing a layer of skill from the game for me. i use grid +clique for major healing spells, the only cd i have in there is lay on hands, all hand spells and stuff i use from my spell ba0r, and im pretty good at it.
when i tank i use very few macros and everything i do i do manually from my spell bar. i use some basic self cast macros like freedom. also some cd announce macros. thats about it. some ppl will say that this is not as efficient as mouse over, and perhaps there is some truth in it. but at worst i am like half a second or 1 second behind in casting an ability and that's rarely a raid wiper, and in the case of something that would be, you can bet you ass im watching for it and ready for it. the reason i play like this, is that i find if i use to many macros and mouse over, all im doing is moving my mouse and not really playing the char and off loading the skill to scripts a little to much.
