Maybe try front wheel gaps, just a normal gap but landing front wheel first, then throw it too back wheel like a wheel swop. Or what about going upto front, say from the floor, your riding in and bunny hopping up, however land on your front wheel on the edge of say 4/5 pallets, shifting your weight forward and leaning right over the front end, then switch it to back wheel, again like a wheel swop. You could also try riding along thin objects to improve your balance, such as rails or wooden planks.