I would just like to inform everyone that doing this to your skis modifies them by compromising the materials, not changing them. The Epoxy used in skis is considered a "thermoset" plastic, meaning, they cannot be melted, softened, changed, etc. They create a permanent bond/shape. Also, Fiberglass has NO elasticity, so by forcing a bend into a ski, you are destoying the effectiveness of the fiberglass, which is the main component of a skis strength.
Just thought I would throw in my two cents before someone ruins their nice skis. If you really want rockered skis, the best way to get them is by purchase, not this. But if they are old shitty skis you don't care about, go ahead.