I have a 2000 Sienna XLE. We just got a floating playpen(pontoon boat) and I put a power winch on the trailer to allow me to lift the boat out of the water without killing myself all while keeping an 18 month under control.

The thing I want to do is to be able to plug the winch into the same light connectors that power my trailer lights, however my lights are on a 10 AMP fuse and the winch has a 30 AMP requirement. Is there an easy way to convert the fuse box to handle the higher load without rewiring things from the front to back. I'm guessing it's not as easy as just replacing the 10 amp w/ a 30 amp fuse and expecting it not to catch fire (IMG:style_emoticons/default/tongue.gif)

Does anyone know of an aftermarket way to just convert the tail lights to handle 30 amps?

Nope. Anyway you look at it, it's going to catch fire. The fuse box can not handle 30 amps, the wires in the fuse box can not handle it, and the light plug in the back can not handle 30 amps.
Your only "safe" option is to run the correct size wire from the battery in the front, to the correct size plug mounted near the pumper. With a 30amp fuse at the battery. You should be able to get a wiring install kit made for your power winch from the winch manufacture. It has all the correct size wire and the stuff you need.