I did something similar (except not in Ireland). I rang up a few local schools and asked them if I could sit the PPL exams with them before doing a full-time flying course elsewhere.
The first call (to an incredibly well known school) was a flat "no". The second, well, they didn't seem to grasp the concept and told me that you had to sit the exams at the same school at which you fly (which is cobblers). The third however, said "yes, come along whenever" and they didn't even charge me.
Be prepared to make a few calls and be prepared for a few refusals.