I would say something like 'I would like to try a long acting med, after so many years of taking daily pain meds that last 4 hours or less, I want off that rollercoaster of pain, to only take a few pills a day and get hours of relief has to be better for me physically and spiritually, if it isnt, doctor, can you please explain to me why not?' He should at that point either offer you a LA med, of which methadone is the cheapest and probably most 'popular' LA med being used these days, or explain why he wont.
If he says he wont and why, ask him at what point he would consider it, if the answer is never, its time to look for a new doctor, but at least you know where you stand.
It is much better for you in every way to be on an LA med than the daily use of a SA one, I wish you luck, dont give up until you are happy with your care! I think if someone needs a daily dose of a short acting pain med for more than 3 months straight, their doctors owe them an explianation as to why they shouldnt be on a long acting med.