(is that simple or what?)
Just use the edge of the cotton plier handle (I tried regular ortho pliers but the handles are too rounded). Make sure you tweak it pretty good to permanently deform the wire, or else you will just temporarily deform it and the inherent memory of Nickel Titatium will work against you.
The video above is of me putting reverse curve in 2 archwires. The first is a 16x22 Thermal Nitinol, the second is a .018 Nitinol. It may take a few times to get the hang of it but after that it's pretty easy. When I first started this technique (Thanks for the tip Dr. Bellon!) I made sure to check if the wires "held" their shape and in fact they do if done correctly.
Besides saving money on expensive pre-curved archwires, this technique enables you to put more/less reverse curve, or unilateral reverse curve!