Need help from the Ins Experts ....please

My doctor submitted a request for the lapband for me, however he is not too supportive of my decision so his referrel request was done on a general form and did not state "medical necessity". There are no Bariatric surgeons in my "network" so I will choose a Dr of my  choice. (hopefully) The letter was not sent to the insurance company because the "network " denied it based on his general referral and not stating medically necessary.  My question is ..since I have my medical records can I get a pre-approval from my insurance company (Aetna HMO) and then choose my own surgeon?  Please help.  I might have to switch Dr's just to have a lapband.