You may wish to call your rich Uncle Arthur, Aunt Claire or other relative. Perhaps you can shake down some of your rich friends too. Otherwise you're asking someone to front you money on an unsecured note on a property sight unseen and without title insurance if what you are planning to buy is going to be auction as a foreclosure on the steps of the courthouse.
If as my colleague Jed mentioned, you are really going to one of these "travelling auctions," advertising on late night TV, you should know those properties are already bank owned (REO) - they have LENDERS ON-SITE who will sign you up for loan on the spot with your good credit. Please note too the whole gig of the "travelling auction" is to drive excitement and overbidding for the owners of the property (the banks.) I personally have seen better deals after the auction is over on properties which did not meet their minimum reserve amount and were reassigned to a real estate agent. (But those deals where in Antioch, Pittsburg, Oakley and Brentwood - NOT in San Francisco.) Then you are buying a REO and you should check out the informative YOUTUBE video link below.
Other than that I don't know what other advice I can give. The few hard money lenders I know are disinclined to lend on this kind of purchase to a stranger off the street. Their interest rates typical for the business are not unlike rates you'd associate with a credit card and appropriate to the risk. BTW You're pre-approval is fantastic and you should realize it is dependent on the appraisal of the PROPERTY purchased along with deliverance of clear title, in short your pre-approval is as good as the paper it's written on.
So go call Mom, Dad, Uncle Arthur or Aunt Claire and pitch your loan. I wish you luck.
Mike Ackerman, CRS, e-Pro
Zephyr Real Estate