The MSP can NOT do interstate transfers. If you want your buddy can drive the gun to a MD FFL, that handles MD regulated firearms, and then you do the 4473 and the MSP paperwork. No need to do anything more.
That's right MSP only do a transfer from MD resident to MD resident. The troopers at the front desk always asked me that same question while going through paperwork.
Otherwise, it's FFL route. If it is close by, I don't see why the seller can not just drive to FFL's place and do the transfer there. I did it several times to buyers in NOVA. Although, if it has to be shipped, "some" FFL will require that it is done FFL to FFL- which is getting more expensive. So, do ask the FFL person you are dealing w/, how he wants it done.