Charlie from Fair City seems quite good at these, try giving him a call, care of RTE.
If not, what about contacting the following (no ties, found in web search, they're a Trinity College campus company)
[broken link removed]
I'd imagine you'd need to supply at a minimum info about parents, grand parents - places & dates of birth, addresses etc, so can you enlist his/her wife to get this info (assuming you want this as a surprise).
The Cost
We only accept commissions where an initial assessment shows there is a strong possibility of tracing your family further.
• Assessment €38 (or US$40)
• Minimum deposit we accept for research is €195
•Standard/Typical research project will cost €360