@panimantare - there is a form called W-7 which is a pplication for IRS individual for Tax Identification Number. Its like a SSN number but not authorize to wok using like as SSN.
You can send this form with all the proof of ur relationship during the filing (it has to be mailed), thats why you cannot file ur tax return as E-file.
Do a google serach on it, should be able to get all the links.