I had not thought about that, but I had wondered about a way to keep them pressed since I recently glued veneer to a kitchen cabinet and used a clamp. That could indeed work! Yesterday, I had put them in the oven again positioned differently so that the mold walls made some pressure; if I can I will give the plastic wrapping a try.One thing that might help is to very tightly wrap each individual bar with kitchen plastic wrap (Saran Wrap or another brand) before you put it in the oven. That's what I did with mine and I believe that held the pieces together like a clamp does when one glues two pieces of wood together.
Dibbles, your soaps are gorgeous. If you don't have time to make new, maybe try the plastic wrap idea after re-wetting the weld sides, and put it in the oven again. All it will cost you is a little more time and some electricity or gas (depending on your oven.)
Glendam, I had not thought of the recipe making a huge difference in this method. Thank you for mentioning that. It would be helpful to know if others who large percentages of hard oils experience anything similar. My recipes tend to be on the lower end when it comes to hard oils. I'll give it a try with another recipe with more hard oils and see what happens.
I don't know if it's too late to try the plastic wrap idea for your soap, but perhaps you could test that out as well. By wrapping each bar very tightly in plastic wrap, less moisture loss will occur during the heating in the oven and it might still give you a better weld. IMO it's worth a try.