Using caps lock key instead of right click (contextual menu)
The 3rd party tool http://pqrs.org/macosx/keyremap4macbook/ seems to be able to do what you need to remap your keys.

One possibility is to remap Caps Lock to Control and thus pressing Caps Lock + left-click would open the context menu.

Sure, this doesn't remove the need for a mouse click, so the right-click might be a better solution :)