Choices
I would suggest you write/visit some local non-NATS units, as they tend to train in-house. Get an ATSA position and then year or two down the line get put through an ADC course and onwards to APC / APR.
The lack of TWR only chaps coming out of NATS is dwindling rapidly, so this would be your best solution.
But as previously stated by niknak units will not be overly impressed if you then leave after all the time and training invested on you, but regioanl airports like NJ, SH, NV, NT etc etc will would give you good experience and grounding. Also think about Finningly they will be recruiting this year and TWR ATCO's and ATSA are the first step for them to get things moving!!
Good Luck!