There's nothing else you can put there that doesn't cause a high same-finger frequency, which slows down typing and reduces comfort. Moreover, the right index finder already does more work than all the other fingers, so putting anything more frequent is not good from a finger balance point of view. The Colemak keyboard layout is also designed to be easy to learn, and keys that move between hands are significantly harder to learn. On Dvorak even a year after learning it, is sometimes got confused between 'T' and 'Y', and it was something I wished to avoid on Colemak.
A better change would be exchanging the 'B' (1.3%) and 'V' (0.9%) to reduce the frequency of hitting the 'B' position. I don't think that 0.4% difference is going to be notable.
Since the change would be rather confusing, and it will break comptability of the shortcut Ctrl+V and Ctrl+B, I really don't think it's worth it. Moreover, the combos AB/BA (stretch for both directions) are slight less common than AV (in the word 'have').
So I highly recommend leaving it as is.