Essentially you are simply asking to keep your loan contingency in effect until the day of funding. No need to negotiate a special clause. This is an available box you can check on page 1 of the Residential Purchase Agreement. Simply tell your realtor you want the loan contingency in effect until COE. He/she should know what to do. That way if you have not locked and rates skyrocket you will be fine.
I am curious though, you should be locked in within a few days after your offer is accepted unless you are buying a new home that is far from completion or you have an exceptionally long escrow.
