In this case, you need the help of a local ATSU. This is best arranged by telephone before departure. You're really asking a favour so be nice.
Huh? Obviously I've always misunderstood the meaning of the word service in air traffic control service.
File a flight plan, pick the ATC unit you call for a clearance wisely (maybe copy them in on the FPL address list and add a comment that you'll request a joining clearance with them), and bob's your uncle.