Unfortunately I'm not sure if this is possible, but I can try. To avoid the ModTerrain issue, though, pull up slightly with the board before hitting an up slope. This is an issue I can't really do much about (even the skis do it); I've optimized the board to avoid it as much as possible. And you can kinda "jump" already by going fast and pulling up, but obviously that's not the same, so I'll give your idea a shot.
Yeah, I've noticed how the snowboard catches its front edge considerably less than the ski's when going over mod ter joints, good job on that one.
would be awesome to see the bunny hop, I'm pretty sure you can easily do it, maybe look into the horse's script?
Oh, and I'm using your snowboard for this little build, come check it out later?
http://forum.blockland.us/index.php?topic=262668.0