How far do you want the master socket moved? Much further into the house, or just on the other side of the hallway? How does the location of where you'd like it to be relate to the existing wiring that comes into your house?
When I had my FTTC service installed, the (Kelly) engineer happily moved the master socket to a new location - however, (a) the old master socket was of the pre-linebox design and so a new one had to be installed anyway, and (b) the new location was in an easy place basically just after where the existing line came into the house from outside.
The standard advice of being nice and polite to the engineer, offering a cuppa and a biscuit, moving any furniture out of the way etc does all seem to help when making an 'above and beyond' request.