Ankesh,

You are in a nice position but if i'm the other guy and hear you're stringin' me along while you try to scratch out a better deal could make me walk.

First of all if he was smart he would've put a time limit to his offer.

If so and you still want to string him along then let Greed solve your problem.

Explain right up to the guy you're searching for a better deal but here's how YOU could win even if you lose.

First if you find a better deal tell him you'll give him a piece of the pie. Doesn't have to be too much but now you've put the guy in a position to get something for nothing. Greed, baby!

So now if you can't find a better deal you still win because you have an signed offer from this guy that's still attractive but also giving you the time to find a better deal.

Might work for you. Remember greed solves all your problems.
I learned that from Vic Mackey of The Shield.