Still no response from the motorcycle reupholstery company in the NE, but I’ve found an automotive reupholstery guy about 20 miles away who gets good reports. He’s willing to take a look at it so I’m taking a run out there in the morning for him to take a look and quote me. Update will follow.
Update 7 Sept - took a nice ride out there yesterday morning to let Rob give my scooter seat the once over. It's do-able to quote him and he'll remodel it to move the bum stop back a couple of inches which will be great, giving me a useful increase in the legroom. Will need it for 2-3 days so we've agreed I'll drop it in at the end of the month for the transformation.
BTW his main source of income is upholstery repairs for the motor trade, but he has another sideline restoring classic cars for enthusiasts. While mooching round his workshop I saw a 1980's Triumph Stag in for a new soft top and seat work and a 1950's (I think) Alvis also in for seat recovering. Alvis is a long-gone marque which used to be manufactured in Coventry just south of where I come from in Birmingham.