You will need to have a DE FFL ship it to a MD FFL.
Don't get me wrong, I'm not basing this on anything but pure speculation for the most part, but are you absolutely sure it has to be handled this way?
For some reason I had it in my mind that as the owner of the gun and a DE resident I could "meet" the buyer at a Maryland FFL and do the transfer there in person. In fact, for that matter, I'm not even sure I see why you shouldn't be able to ship it to the Maryland FFL yourself.
Basically I'm looking at these two sections of code... (from the ATF FAQ)
[18 U.S.C. 922(a)(3) and 922(b)(3)]
A person not licensed under the GCA and not prohibited from acquiring firearms may purchase a firearm from an out-of-State source and obtain the firearm if an arrangement is made with a licensed dealer in the purchaser’s State of residence for the purchaser to obtain the firearm from the dealer.
Which would seem to imply that as the out of state purchaser the arrangement has to be made through a dealer in my state... That we know... The question I guess comes about getting the gun TO that dealer... Which brings me to...
[18 U.S.C. 1715, 922(a)(3), 922(a)(5) and 922 (a)(2)(A)]
A nonlicensee may not transfer a firearm to a non-licensed resident of another State. A nonlicensee may mail a shotgun or rifle to a resident of his or her own State or to a licensee in any State. The Postal Service recommends that long guns be sent by registered mail and that no marking of any kind which would indicate the nature of the contents be placed on the outside of any parcel containing firearms. Handguns are not mailable. A common or contract carrier must be used to ship a handgun.
I dunno, again I'm far from an expert, but to me it sounds like as long as I arrange it with the FFL in their state I should be able to either hand deliver, or ship the gun to that FFL, who would then do the FFL transfer to the buyer. No?