Speaking as someone with personal experience with this, as well as professional experience, I think the most likely scenario is that the broker/agent, and/or the seller's attorney, would **strongly** advise the seller to reject your proposal.......and perhaps any other proposal you might bring forward in the future.
It can be very savvy, especially if you're an investor, to put down payments on numerous properties and then actually buy the only one that gives you the best deal, letting the others go. This is one of the many games that just aren't played in Manhattan (don't worry, we have our own set of unique real estate games ;) )
With money market rates hovering around .6% if you're lucky, the opportunity costs of your cash are minimal. Everybody in the transaction knows this. So the only reason you want to put down less is so you can walk away easily. (The only other possible scenario is if you're a foreign buyer who is getting a loan overseas, without disclosing in the USA, and are having trouble getting that loan. Still not good for the seller.)
If you really want this property, I would not even mention this proposal, for fear of being bounced out of the room. If you're not sure you want it, then I would wait until you are sure, and plan on putting 10% down.
Lic RE Salesperson
Charles Rutenberg LLC