The only solution is to get more Wiimotes. It is really unfortunate, but it makes Nintendo money. You need one Wiimote for every Classic Controller that you want to use.
I highly doubt that a port to the Gamecube controller socket would work, but if you manage to find one, then go ahead and try it. But my common sense tells me that the controller requires power from the Wiimote, and is not going to get power from anywhere else.
I would suggest getting a Gamecube controller if you can find one. It's similar to the Classic controller, and it plugs right in to the GC controller socket. That's what I use. It's also good because Ii don't use the Wiimote's battery.
Good luck
Been away for a bit, but sneaking back in.
Gaming on: PS4, PC, 3DS. Got a Switch! Mainly to play Smash
