Well, I dont have first hand experience in this [pun not intended], but I belive you go up the rear with a few fingers.

Is your man considering this also??Most guys are really freaked out by this and unless he knows its coming(no pun) be prepared for a full blown wig-out.I don't know if you are m or f but my experience with 96% of straight men,they don't want it at first.After they get over the initial shock/fear they find it to be a great orgasm.Go easy and be well lubricated.You'll feel a smooth protrusion in the rectum-that's it.Oh-no acrylic nails!!Very unsanitary!!