See if you can move the engine forward on the engine mount.

If you need more than 2 ounce of lead... try using a brass "acorn" prop nut. This puts the weight as far forward as possible... meaning you need less weight.

ANYTHING you can drop in around the fuel tank and pack in with foam will work for ballast.... I've used dead alkaline AA cells, nuts, bolts.... even small rocks picked up at the flying field. BB's mixed with epoxy do really well too.