throttle body

the screws for my 96 silhouette IAC valve broke off in the housing, I have all the bolts out except for the far back one under the trans dip stick, the bolt turns but won't break free, I can't seem to get a wrench on the back side of the retainer" bolt, it's too thin and not enough space for a socket, is there a special trick (aside from a sledge hammer) to hold the bolt on the backside so I can break it free and remove the throttle body??? please give assistance, thank you