Man, I seriously have problems believing you wouldn't put up with the (emabrrasment? is that it), or taste of Barium to find out whether you have 6 months, or 25+ years left, or whether they can prevent the 6 month option from occuring. They wouldn't even "stick a finger in your butt", it would almost certainly be a referral to a specialist, and they would generally use a proctoscope. If you live to an old age, it's a standard checkup item, so if old age is what your'e after, give it a go.
The doctor is there to help you, but you need to ask for the help first.....