Lol... It is possible for every btm to cum while being analed. as long as the top's dick stimulates the btms prostate(P-spot" or the "male G-spot) while fcuking him. In fact, you can just cum by giving yourself a prostate message. without any physical contact with your dick. The prostate is located 2" (5cms) in on the front wall of the rectum. So a finger can be inserted to feel it (just as the doctor does in an examination). You will feel a chestnut sized swelling which has two halves. As men age the prostate becomes larger so it could be the size of a pear. Conclusion: same theory as the prostate message, as long as the top is able to stimulate the p-spot while fcuking the btm, auto cum is achievable.