It must be really sticky stuff!
Try the aloe vera it might help to loosen it as it's an oil. Also use your thumb to hold his feet down then he won't be able to push you away if you still wanted to try and wipe him yourself while hand holding him. If he's preening away he should remove it himself very gradually just keep spraying daily or bathe in warm water to loosen the stickiness. The smell will leave eventually and as long as he acting healthy again that's the main thing. If it's causing problems maybe take him back to the general vet and ask if he can clean it off. Spray daily and give him the opportunity to bathe in warm mineral water and he should be fine.
Hope that helps
