The biggest hindrance you have is being currently employed; that fact alone makes it really difficult to pronounce a SEH. It's not impossible but difficult. Here is the TLDR for getting premed+med school in one shot: you need to convince your VRC that A) ANYTHING other than being a doctor will NOT be consistent with your interests, aptitudes and abilities and that B) you have one or more SCD's that create this situation for any job other than being a doctor. How you spin that is up to you but that is the criteria you need to justify. The goal of Ch. 31 is "entry level employment" in a field that is consistent with the veterans interests, aptitudes and abilities (including SCD's). If entry level employment is being a doctor, that means any individual rehabilitation plan must include the necessary degree to be gainfully employed in that field. It's really like a giant logic reasoning puzzle that you need to meet the criteria for.
An argument from your end might go like this:
I'm interested in radiology, I've demonstrated an aptitude for it from my current employment/past training/testing etc., BUT my SCD relating to my knees makes the job untenable. However, as a Radiologist, I can continue to purse this interest without the mobility duties associated with a being a tech. No other job will fulfill this criteria except radiologist. Entry level employment requires an MD or DO degree and thus my rehab plan should include one of those degrees.
If you go in all wishy-washy saying "I'm going to try for either PA or MD" and "I'm not sure what kind of doctor I want to be" your VRC will eat your lunch. They'll smell blood in the water and know they can steer you out of their program with only a few months of Ch. 31 and be done with you. Whether you really become a radiologist, go to PA school, etc is of no consequence to
how you actually present the case. The case argument needs to be rock solid, highly specific and immutable. That's still no guarantee of approval but it greatly increases the odds your VRC will start to bend to your will, instead of the other way around