Let us know how it goes Nathan.
I had an idea for ya.
Go to your local Walmart in the sporting dept and pick up a packet of Wrist-Rocket slingshot lead . Forgot what each ball weighs but they got to be at least 1/2oz . Then make a small slit midway in the left wingtip and drill a hole straight in maybe an inch to start with. Insert a leadshot or two and try it. If it's not enough to straighten out your loops then add another.
Plug the end of the hole with a plastic cap and a little foam safe CA. Use some of the extra red vinyl you got with your plane and patch the slit. What do you think ? Better than those darn little Great Planes 1/4oz bricks of lead with adhesive tape ready to fall off on your friends as you make a high speed pass. Plus only you will know about it. Or just invert the motor like you said. lol