Of course the best solution is to get your other half to do her test and get her own bike
Liz sits on the back of my GSXR one had through the strap on the seat and the other hand shes been know to use to text on her phone. I'm pretty sure I'e also felt her go to sleep on the back to. Normally I dont even notice shes there.
Sounds like your other half isnt very confident on the back of the 675.