The only thing I can suggest is to use something less common like F11 & F12 or something.
It's not that it adds to the specific key what bothers me, but that it adds to the total.
I'm thinking... there's Mouse button 1, left click, 2, right click, 3, middle scroll click, then 4 and 5 the side buttons this mouse has. Maybe there are Mouse buttons 6 and 7 too or something similar?
Edit1:I just remembered, since I'm using modifiers on the mouse buttons 4 and 5 now these are unused, so I can just put these on the thumb scroll. Silly me.
Any news of the AltGr fix though?
Edit2: Oh man... that actually didn't work... since as long as I have Xbutton1::ctrl for example, and the thumb scroll indentifies itself as exactly that, it now acts as a ctrl...
Edit3:The only thing I could think of, is for you to disable on the counter 2 buttons such as browser forward and backward, I bind them to the mouse button 4 and 5 using the mouse's software, then, using autohotkey, I make something like Browser_back::ctrl, and for the other alt, then mouse button 4 and 5 are free to use for the thumb scroll.
Edit4:I binded those like I said, now all I need is a version of the app without the browser forward and back. Could you make one for me please?