nervous

My wife is a bit old fashioned (maybe a little prudish) in the bedroom. I have occasionally gotten her to try something new (very rarely) but it never lasts. For several months now I have been interested in eating a creampie, but don't know how to approach the subject. Should I talk to her about it, or just go south after I cum. I usually give her an orgasm by cunnilingus before intercourse, but I have been wondering if waiting until after might make her more receptive to my desires. If anyone has any suggestions in this matter they would be greatly appreciated.