You could probably do that, however, without knowing exactly what motor year you have, I do not know for sure if it will work.
Hardwiring the wiring to the motor would make it difficult to remove the motor from the boat, without disconnecting the wires at the various parts of the motor. A plug at the engine that mates with the boat harness would be much better, even if it is just bullet connectors.
If it were me, I would look at a wiring diagram of an engine with the skinny 7 pin plug and see what what wires it has, versus what wires you need to operate your motor. You probably don't need engine killer wire, but probably need ignition power to run your ignition system. It is a guess..