Its not like Farnborough LARS is a "centre" itself, seperate from any airport or area centre. The LARS's are delivered from the radar room at Farnborough Airport alongside the approach radar controller for Farnborough (infact a lot of the time its bandboxed). The ATCOs providing the LARS's are also qualified to control in the tower at Farnborough. The room they control from would be there anyway so no problem really!
Like someone said before, instead of NATS paying band 5 ATCOs to provide the LARS from Swanwick, NATS can pay band 1 ATCOs (who also double up as tower controllers) to provide the services. Its kind of two for the price of LESS than one if you see what I mean.