Maybe he meant, "Sister Imelda, the Blue Nun" as if he was listing them, meaning to say that Jack used a bottle of Blue Nun wine to get Sister Imelda pissed and then had his way with her?
That, or Sister Imelda is the Blue Nun and is a naughty so and so and her and Jack got up to some interesting antics at the wedding in Clones (which is in County Monaghan in case anyone was wondering!)
Or maybe JAck just was a randy beggar and used a bottle of Blue Nun on Sister Imelda in a 'Kinga' kind of way?