Correct me if I am wrong but... Whatever is outstanding on your loan, I believe you can claim for. In your example, the $2000 that you have spent you have already paid tax through your personal income even though it didn't come off your loan you are still getting interest on the outstanding balance. Therefore you should be able to claim anything outstanding on your loan.
I don't really know and you should really consult an accountant or tax agent. But that is the way I have been doing it :)
