How about pressing Return key?
I've got a weird set up @ home that's evolved out of trying to fend off carpal tunnel. So it's not so easy to get to the return key.
I'm surprised we can't double click to commit transform.
You should be able to click insde the transform handles to commit the transform or switch tools.
Depending your mouse driver you might be able to assign the enter/return key to the middle mouse button.