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Thanks for asking!
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