virtualbox.org

It is a bit of a pain to use the right-ctrl button to release mouse capture. I know I can set the host button to any key on the keyboard, but is there a way to map it to the middle-mouse button?

I've never read or heard of any such thing in the Virtualbox settings. I do know there's software to reprogram mouse buttons, though. Could such software make the middle mouse button behave like right-ctrl? And would such software retain control over the mouse input when the mouse is captured by a guest? Yes to both ?'s might make such a thing possible even if Virtualbox doesn't have the capability built-in.

I have my doubts this will work. You would need to have the guest middle click register on the host not the guest. It may be possible to get it to work with a host program but the mouse integration would need to be considered.