I can't tell you for sure, but if you can take the heads off and reverse them (I think you can with the besseys) you should be able to do what you want. Most of the pistol grip clamps, like the Irwin Quick Grip, can e reversed.
Let everyone know what you are doing. There's a lot of experience here and some one may be able to help with some advice.
Thanks Ed I'm making a quilt rack as luck would have it I measured twice, dry fitted, and my bottom stretcher still came out a little long. So to save the project I cut the stretcher off routered the tenons flush to the sides. I will make a new one with short dowels on the ends to reglue it in place. Here comes the need for clamps for stretching. My Besseys are the older model I'm not sure heads come off. I may just buy some new versions. Can never have too many clamps right Ed!