It would certainly be possible, but I'm not sure it would solve a
problem. Even if dismiss is small, it would always be easier to hot
this button then solve captcha afterwards. So the only think it could
prevent is accidentally pressing the dismiss button. Perhaps a better
solution for this problem would be, that you can also get back to
snooze mode even when the captcha is displayed? Then if you press a
dismiss by mistake, you can still revert this mistake (as long as you
are using captcha).
Cheers,
Martin