Sale deed pending for originals collection

The seller has pledged his land to a private bank, and I (buyer) have done the full and final settlement (around 90% of sale consideration), a part of the amount on the sale consideration. The private bank will be returning the originals to me in front of the seller (private bank has given same in consent letter), in couple of months time, once they receive it from head office. Now I want do sale registration, but seller says their negotiation is not complete, and need more money to come for the registration (although the initial advance agreement in 20 rupees unregistered stamp paper mentions the final amount clearly). I suspect this seller will keep asking extra money for every next steps that I want him to do, like coming for originals collection, coming for sale deed, etc., I want to complete the negotiation once for all, and quickly remove the dependency with the seller. What is the option I have?. Can I do registration along with pending sale deed when I hand over this negotiation amount, or is there any other better options to get the land.