How can you get a building permit before you own a house in Danville,
Ca.? We are in contract for a house and have gotten the sellers to
agree to a 75 day close, because we need at least that amount of time
to get the permit. Since we won't own the home til 75 days from now,
how can we apply for the permit in the owners name?  What is the
lanaguage we need in the contract to make this happen? What are the
pitfalls?
transfered?

Would the present owners be willing to submit the plan in their name,
if you do all the work and pay for it, of course?  This site says that
building permits are valid for a set period:
http://www.ci.danville.ca.us/default.asp?serviceID1=432&Frame=L1

Of course, you would have to accertain whether approval is restricted
to construction by the person submitting or is valid for a new owner. 
A phone call should be able to clarify that  - or a way to arrange for
you to step into the approval, maybe by submitting a duplicate request
immediately on purchasing with reference to the one already approved.