I remember before they shrunk from HRT, mine would slide out too. I found stuffing them up, folding the thing back and stuffing the loose skin they were sitting in up there as well and then wearing something tight to hold them in place (cutting off the legs of some control-top tights and and using the panty works well for this) should give you a fairly smooth appearance. There should be no pain, because if there is, you're doing it wrong. I've found this technique works well enough that even just last night I was standing in the women's dressing room (for my musical) in just tights and a bra and you could not see anything but smoothness there. I probably could have done it in just underwear, but I wasn't going to risk it showing. 😛