DFC you are making a mountain out of a molehill - again!
So if I am in my aircraft on the ramp and thus no longer able to access the telephone or terminal in the Flight Briefing Unit, you are going to simply say "hey buddy, call back the bus, take 30 minutes to get back to the FBU, send your message, get an ack/slot and get the bus back to the aircraft".........whereupon I am now back at the aircraft 30 minutes after my original EOBT.
You just call your handling agent / company on box2 (or mobile phone etc...you get the idea) and tell them to send the necessary messages on your behalf. Look - it's that easy
It quite clearly explained where our respective responsibilities lie here:
http://www.ais.org.uk/aes/pubs/aip/pdf/aic/4Y146.PDF
Not doing your work for you on a regular basis is not being lazy. Do it for one you might as well do it for all and that kind of undermines the whole point of allocating responsibilities.