[i_gothere]

Basically, what you have is the good old Eircom shove-it-till-it-hurts-and-hope-they-stick-with-us routine.

Fact: Eircom must install the line. Unless you had an arrangement with your builder that they provide the lines, you're not going to avoid that. Sorry, wish I could say better.
Fallacy: You must wait x weeks for Smart to be "permitted" to take over your line. Fact is, you can do it same day if smart are available to you (I have done so twice in the past, though not with Smart). Eircom want you to give in, they're pretty well rehearsed on that schtick.

Just be bull-headed about it. Get the line installed, and even while he is there call Smart and have them take over. At that stage you have a connection point in the Exchange, so there should be no problem.