In theory it actually isn't that hard. Without checking, if my memory is correct, all it is, is a correct resistor between one of the signal pins and ground to signal the maximum amperage draw. BUT the tricky part is that the only place you have access to the signal pins is the adapter part that plugs into the shorter UMC cable. ie. it is the short stubby Tesla 14-50 and 5-15 adapters that have those resistors in them. To make a "real" 14-30 adapter, for example, you'd have to make a connector that mated perfectly with Tesla's proprietary UMC plug. That just isn't going to happen.