This was discussed very recently. If I remember there is little difficulty nominating a PRSA provider and then providing the employee agrees quitely ignoring it.
I am in the same boat. Got a questionnaire from the Pensions Board and after speaking with my accountant (who intially told me I did not have to bother with a PRSA) it seems like you have to designate a PRSA provider but you do not have to do anything with it. ie no requirement to make payments.
However I imagine whatever company you choose may bombard you with literature etc ...