I'm convinced it's possible to get the dump truck up there. I've gotten sooooo close.
With the tractor, the trick is just to do burnouts then release the brake, it shoots forward
hahaa....yep....never tried the sticky bomb but RPG's, Helicopter/Plane Missiles and putting vehicles in front of it doesn't seem to do much...
I think it might be a single player mode thing...not sure about Online.