I believe (not having tried it myself) that you will be unable to file electronically, but will have to print and mail your return.
The reason is that the IRS instructions for Schedule A clearly state that not only are you to provide your SSN to the buyer, but the buyer is required to provide it to you - failure to comply can result in a $50 fine.
"
Line 11
If you paid home mortgage interest to a recipient who didn’t provide you a Form 1098, report your deductible mortgage interest on line 11.
Seller financed mortgage.
If you paid home mortgage interest to the person from whom you bought the home and that person did not provide you a Form 1098, write that person's name, identifying number, and address on the dotted lines next to line 11. If the recipient of your home mortgage payment(s) is an individual, the identifying number is his or her social security number (SSN). Otherwise, it is the employer identification number (EIN). You must also let the recipient know your SSN.
If you don't show the required information about the recipient or let the recipient know your SSN, you may have to pay a $50 penalty."
If you print and mail, this gives you the chance to write a short statement as to why you can't supply the SSN but do supply the seller's name and address.
