Talkdownman:
Secondary working in the case of part time employment?
If you (or anyone else) is also employed as an ATCO elsewhere, it's extremely unlikely you'd be able to meet unit currency requirements, comply with SCRATCOH or, realistically, remain at a competent level of currency at either unit, especially if the NATS post was as demanding as, perhaps, Farnborough LARS.
As far as I understand it, with airfield operations, SRG will only grant dispensation for a second validation at a different unit, for the purposes of leave relief and then only the most onerous of circumstances.