The easy way, would be to fax / email SB the GAR form min of 12 hrs before departure from Booker. That is all you NEED to do to GO TO Southern Ireland.
On the way back you need to tell Customs too (12 hrs notice before arrival back for CU and SB), so what I'd do to cover my arse is fax / email the GAR to SB and Customs in one go before departure but also indicating return dates and times on it if known. In other words 1 email, 1 GAR copied to SB and NCU, with both departure dates and times and arrival dates and times on it. Don't expect a reply though!
I filed my FP using the AFPEx website - brilliant it is too. You could then stop anywhere you want enroute - Havaford West for example.....