I'm really against the idea of shoving objects into your mouth to practice. This will allow the dude to get far more physical than he would otherwise, increasing the chances of female damage. On the plus side, the fact that he's still with you even with the troubles in the bedroom show that he's a reasonable bloke. My bf is another member of the huge penis club and I can give you some tips that we use. The only problem I have is when people rationalize it in such a way that it eliminates any responsibility they have for the other person's feelings like so: Answer 2 from a man: I'm not sure anymore!
The object is to give him feeling but to keep her safe from having her cervix bumped as he thrusts with his long cock.
I've had a someone vomit on my penis. These are real issues for men with massive length or girth. This'd be close, in size and shape, to an actual donut and made out of foam. Since I'm considerate, I whispered, "Look, we can stop if you want. It definitely helps if he's willing to make you come first before entering you, or even if you're willing to just finger yourself while you give him oral.