Now who could possible know where most of these people if they still live in Ireland might be? Why the tax man of course! The revenue has the current address of all taxpayers in the state. Now if the colleges to send on those PPS numbers of graduates to the revenue naturally with the money to cover the cost of one envelope per voter containing a registration form and a prepaid envelope address. Then the revenue could send same to all those PPS/RSI holders they have on record without any concern about a breach of confidentiality. That solves the other side, identifying where people live.
Combine this with automatic registration at graduate ceremonies and we could expect to have an accurate and up to date register instead of the poor condition it is right now. Such measures would increase the registration level from pitiful 30/40% to closer to 90% in my view.
All the information is there in the system it is simply a matter of making best use of it.