Yehudi Gordon tells you how to do perineal massage - I think you slather on the oil, put one foot on the side of the bath, and give the whole thing a good kneading between fingers and thumb - you can feel the band of muscle that needs working. I think you are aiming just to get suppleness and bank up the lubrication - I don't think you need to stretch it to baby/turkey size in advance
Plus, (if I remember rightly as its been so long) you have a thin bit of skin there which is obviously tighter than the muscle and so tearable.
My cat is very small you know and I have been sizing her up for a while wondering if she would still be the smallest in the family, or whether the new born baby would be smaller - and I'm afraid the cat is going to remain the family tiny thing.
Probably just as well for the cat or it could end up covered in all stretching my perineum....