It looks to me like only the panel dimmer really requires the ground. I'd have to go test to really be sure, but the service manual print doesn't indicate the switches really need to be grounded. The dimmer shunts power to ground to reduce voltage to the dash lights. Some wiper switches (3 speed?) have a filter cct that ties to the ground but mine (2 speed) doesn't. The headlight switch - unless it has an internal relay, doubt it - doesn't require a ground. Rear window defogger definitely doesn't need it. The real trick would be to use switches that duplicate the original. Just tested my headlights ungrounded and they work fine.
