GB , is right . You have really got a nightmare that every turkey hunter could be in. This may take you a few days to hunt. Aggression maybe the only link to getting the birds to cross the creek. They may fly across before a roost time , if their interests have been taken. There are so many angles that could happen here.

With the easyest, just going and asking permission to hunt the other side.
Decoys maybe wirth a try ,in an opening close by the creek for the toms to see.

Working the birds right at first light , if they roost close by the creek and pitch out of the roost and glide across in the air. Wish I could be more help, but I'm road blocked on this one aswell....BT