A better question to start out with might be: why do you so desperately want to try something that is far more likely than not to hurt your partner?
I have nothing against anal. As a fantasy, I think it's hot. But is it fair to ask someone to do something that is going to cause them a great deal of pain?
What your answer is to the above question may change "how [you] persuade [us] ladies into a back scuttle."
Is it just a hot, kinky thing (as I gather by your post)? Is it because it's tighter?
If it's just a kinky thing, maybe you could try some toys yourself, first - to get an idea of what it feels like yourself and get into the kinky mood. Seeing you take it first might make her feel more willing to give it a try.
Rookie Scribe