Right off the tp of my head I would use a syringe filled with olive or vegitable oil and inject it into your bum. It's amazing how slick anal is and the feeling is mind blowing because you feel every bit of the friction without the drag. It's very very messy though. I would suggest doing it you in an empty tub, which could be even more fun cause I could rub the oil all over your body too. And with the oil being edible all oral possabilities are safe fun.
If you are feeling really adverturous, a urine enema is an option.
Do you like cum inside you? If you do I can suggest a few fun things to expand that realm of possability.