Rubber bands on a wing are the only way to go on a trainer. I have seen many trainers cartwheel on take off, and it's not a big deal--unless they are bolted on. Then, not only do you have to "re-do" that one hour it took to convert them, you have to do some major repair to the center of the wing and probably the fuse.

Thor,
I had it happen to me, but with much worse results. I generally flew with 8 rubber bands. I read an article about "How to fly in the Wind", since I live in a windy state, it was often said at the field, "If you can't fly in the wind, you can't fly too much here." So I was determined. Read the article three times, and just waited for the first 25 mph+ day to try out my new "skills". I remembered everything in the article EXCEPT the paragraph at the very beginning of the instruction that said "Always use extra rubber bands." I taxied out, with the elevator down, ailerons down correctly, swapped them in the turn, and off it flew. It was doing great, I was really getting the hang of it. Brought it in for a landing, touched down, ready on the controls, took off, and then really got brave and started doing manuevers upwind and downwind. The wind kept getting stronger and stronger, and was probably 30+ with gusts around 45mph (strong enough to rock me on my feet). As my confidence built I got more daring, and as I did a full speed pass down wind, I suddenly got curious as to how quickly it would slow down if I did a 180º turn back into the wind. I yanked the wings over at 90º, pulled all the way back on the elevator, and leveled it out. It nearly came to a stop, and I saw (what I eventuallyl found to be the plastic left wing tip) fly off the airplane. As I was trying to figure out what it really was, my first thought was it had ripped the covering off, the plane suddenly nosed down about 45º and headed for the ground. I was so dumb-founded that I never did pull back on the throttle, but almost ripped the elevator stick out of the radio. In a matter of seconds it disappeared behind the trees. When I found it 10 minutes later, it was literally stuck in the ground with what was left of the tail sticking in the air. The impact was so hard, that it had pulled the tail-feathers loose from the fuselage, and all three were bent forward. The engine and about 3" of the nose were imbedded in the ground. Fortunately, it had rained the day before, and other than a crushed spinner and prop, the only other damage was a crack in the case around the carb. When I finally looked at the wing, there was one tip that needed two ribs and the balsa sheeting replace and the covering. It was in amazingly good shape. All the little pieces fit in my jacket pocket. What the post mortum revealed was that not only had the wing been lifted up, but moved back until the control rods stuck into the fuse about an inch behind the wing seat. That had changed the DG, eliminated any possibility of control. Pretty weird in my opinion.

The moral is, rubber bands aren't bad, just use plenty of them. The one for every ½ lb sounds pretty good--unless it is windy! :-). I hope someone else learns from my mistake.