Registration of property on Father's name

Hi,
I have bought a under construction flat in January 2011, and Sale Agreement was executed on my name. Total worth of flat as per agreement is ~34 lakhs as per the agreement. Out of 34lakhs, my father paid 20 lakhs from his GPF money and I have taken a loan worth 14 lakhs from SBI. Construction is about to complete and we have to register the property. I was planning to register the flat on my Father's name, but since sale agreement is on my name, SBI have reservations on that as they have sanctioned me the loan on that sale agreement. Also my father being retired employee he can not be included as co-loanee.

Can you please suggesst me some options here:

1. Since my father has paid major share of money 20 lakhs from his account is it possible to get the flat registered on joint name instead. Will I have to get new sale agreement done for that, to include my fathers name in that? My builder is ready to issue new sale agreement provided bank gives NOC.

2. If I get the flat registered on my name, is there any way a affidavit can be included saying I have borrowed 20 lakhs from my father and until I pay that I do not have ownership of the flat.

3. Actually getting these things done is bit tedious through SBI, so I am plannnig to explore the option of loan transfer to other private banks, who are more open to weak the things to gain customer. And they are ready to accept new sale agreement on joint name.
Any other solution in this matter will help me a lot.

Thanks