i had that same problem during the presales, and i phoned Ticketmaster -
they told me that if you choose Ireland as the country of delivery,
the form that then appears allows you to enter whatever your real country of residence is.
i didn't actually try this myself, but that's what was suggested.
if you feel better phoning them, a number that actual human beings eventually answer is:
++44 161 385 2111 (that's for people calling from outside the UK)
it says the lines are open monday - friday from 9 am to 8 pm and saturday/sunday from 10 am to 4 pm.
if you do phone them, it would be a service to humanity if you pointed out this error on the ticket-buying page and asked them to fix it ...
"What do you want - what?!"
- Keith