Wow, "approval" since August. What a mess! As if foreclosure wasn't hard enough, lenders have to drag their feet and torture home owners even more.
If you cannot get them to postpone the auction, I would advise your buyer to attend the auction if they want the home. As long as their purchase price is going to cover the loan amount (or maybe a little more) then they will just be competing with the bank (which they are doing right now anyway).
Another option is that if the property is sold at auction. The State of Michigan allows a 6 month redemption period. So what you do it get the money from your buyer (needs to cover the redemption costs), payoff the amount owing and then transfer the deed to the Buyer.