Route the battery cables out the side of the fuse. Plug in to turn on, unplug to turn off.

Or get a switch rated for at least the amperage you can deliver from the local shack, and solder it into one of the wires from the battery connection to the speed control. Shouldn't need any extra plugs. Just cut and solder the existing ESC wire. Either one should be fine, though I switch positive out of habit (automotive taught me to use negative ground).

J