Yes, I sometimes use an older Zumo 345 LM as secondary GPS.
I plug it in a 12V "cigarette lighter" socket that is connected through a switched power relay and fuse box - so not hard wired.
One could even try to plug the provided usb cable to a usb outlet, but in the past I experienced some problems connecting a GpsMap60 with a generic cable that way.
Using the 12V plug shouldn't be a problem.
You could even move your other connections to a fuse box, but I guess that is not what you asked and is probably described in another thread.
Best of luck,
Ed.