This won't work.
When you PM with AMEX BVG, they will verify the credit card transection.
If they see that BestBuy credit you back $60 for the same transection (yeah, the transection # will be the same), they'll put it into consideration and only give you $75 - $60 = $15. Which is about the same as the original $149 - $75GC deal.
The only exception this would work is that if you can get AMEX BVG send you the check first, then go back to BB and do the PM with CC for the $60 difference. But I think by the time you receive your check from AMEX, the $149 price at CC will be long gone.
Good luck if anyone wanna try it out.