Hi again Barry,
In case it makes you feel any better, I was thinking about you during lunch. I actually don't think the forms should be terribly complicated, if I understand the situation correctly. Once you get your ITIN (and surely there must be a way to get that without sending off your passport?), you could probably fill-out the 1040-NR by hand since it will almost all be left blank. The first section is all about "effectively connected income" (payment for work you did in the USA, etc.), which I imagine is all blank for you. On Schedule NEC (Not Effectively Connected) you will put the capital gain, and, if I am right about you not needing to pay any capital gains tax on it in the USA, you will put it in on of the "Other" columns, and specify the tax rate as 0%. You will put the amount of tax you did pay in the appropriate place on the 1040-NR, this will subtract from the $0 that you should have paid, and the result will be that they owe you a refund of the tax you paid. I imagine that the numbers you need should all be on the statement that UBS sent you - I think it should say what your capital gain was, and what tax you paid on that. The only problem is that you are past the filing deadline, and I don't know what the procedure is for that.
Also, don't forget to declare the capital gain on your Irish tax return.
So, unless there are other complications, hopefully it shouldn't be too bad.