Only a tax practioner can guide you properly in this matter. However, a separate account (other than existing one may be opened) with borrowing Bank, after intimating them your difficulty. Accept crossed cheques only into the account. Pay the amount through cheque/demand draft to the Builder obtained from the same branch . Do not operate the account further.
Another way is asking your friends to deposit that amount in their individual name in the same branch. Avail a deposit loan/Overdraft and pay the amount through demand draft to Builder. Inform that in view of the escalation in stamp duty, and as the loan formalities require time, you are constrained to raise deposit loan and get the Registration, and request the bank to credit the amount to the loan/overdraft acount.
Close both accounts immediately after the purpose is served. There is no difficulty for you, but your friends should have proper account for the money being given to you. Most important thing is that your Bank should accept for this arrangement. If loan is not sanctioned, what has to be done has also to be considered.