I am an auto electrician
Still can fit a socket where there isnt space for one though...lol
Before attempting. THIS WILL VOID WARRANTY FOR SURE AND SO WILL ANY OTHER TAMPERING WITH ELECTRICS. YES EVEN CHANGING WATTAGE OF BULB WILL VOID WARRANTY DUE TO EXTRA HEAT EMITTED.
There is the same ammount of space as the other cluster where one is fitted. Just take off the cluster, drill a hole (the size of the socket thread) in the same place as on the other cluster. Insert socket from inside cluster (or outside depending on individual design). Screw on rear of socket (or front if as before design is other way round). Wire it up (you should know how to do the last bit).
See socket below. Available from any hardware store.
P.s. Don't forget to seal it.