We were in the same situation with my wife. While she is not going ride Ragbrai herself she is going to meet me during Ragbrai so we are purchasing her a non-rider wristband. The problem is that as far as we know and understand you cannot get a Support Vehicle Pass unless she is registered as part of a group. For that I believe you need three or more people registered in your group according to the rules. No all the people registered in your group have to be riders.
Jason