The Honda1300ST looks like a big beast.
What you say about riding the bike WITH him makes total sense.
I used to ride horses, if you just sat on those, and didn't lean away from the bend and stay uprightish (totally different I suppose?) you fell off. I used to get accused of having been a biker cos I tended to lean into the bend.
Would riding the bike (Honda), in moderation, actually be useful exercise for your lower back?
It would be really good if you could have a go on the Goldwing with his employee, then you could see if that worked for you - (the bike not the employee)
Mind you it still doesn't help with Bobbles wanting to make the most of the sports bike, which as you say is totally understandable.