NewtoSD – Since you are buying a new home you are working straight with the developer I assume. You can talk to the developer to see if they will let you keep your loan contingency until closing. Unfortunately I doubt they will.
Most people who buy from developers simply float the loan rate until they get within 30 days of closing. Then they lock the rate at that time. This does leave them susceptible to rate fluctuations that could be quite harmful if they flare up at the wrong time. This is always the risk of locking into a purchase months before coe. Like I said, try to see if they will let you keep the loan contingency until coe or right before coe. Chances are they will not but you can try. Otherwise see if they will let you have a long lock period, I assume you are using the preferred lender to get your incentives. Alot of the time they will have programs with an early lock and a 1 time float down in the event rates go down. They charge you for this but you may want to utilize it.
Also, it is unfortunate but many people get blinded by the incentives and rush to use the preferred lender rather then considering an outside lender to get a possibly better rate.