Remote Buddy's drivers are all closed source and compiled directly 
into Remote Buddy for the time being, so I'm afraid you can not 
extend it for now.

I do however intend to add support for more and more features of the 
Wii™ Remote as I find time to do so. Remote Buddy's internal 
structure does allow for multiple button presses. Right now, the WR 
driver does seperate them to subsequent press / release events to 
avoid unexpected behaviour of Behaviours (i.e. if you press left and 
up at the same time in an application whose actions send f.ex. Ctrl + 
A and Shift + Command + H respectively, you'd end up with Ctrl + 
Shift + Command + (A? H? Both?), which could trigger a totally 
unwanted shortcut.

I'm looking into some interesting options, though, to expose multiple 
button press functionality for those that want to use it.

Best regards, 
Felix