I've tried before and he runs away .He has no say in that, time to learn to do it. I knee on the floor, with the rabbits rear between my knees and one hand on the face to keep him from going forward. For the back of the rabbit I turn it around so that he get stuck under me and stopped by my feet. Wear sturdy trousers you don't like much, and shoes.
Most important though: Always have a treat ready and give it right after you've done whatever had to be done.
Simethicone does nothing against fur buildup, and neither do any fruit juices. Since stringed poops come out and he's still eating stuff I doubt there's an actual problem there right now, but brushing a molting rabbit is a good idea.