This sounds like a really good idea and I'd be happy to participate. However, having seen the unexpected things which can go wrong in even the most professional of workshops, I think some sort of disclaimer would be needed to protect the provider? In theory doing a simple code reading or service reset would seem, taken at face value, to be pretty risk free. Whereas doing a proxy alignment (which I've never actually done) could carry risks? there's also the "unknown factor" in that this will be a vehicle of unknown provenance to the provider who might be accused of "wrecking" something - It would be very difficult, and a load of unwanted hassle, to prove that it wasn't you that caused the problem?
Sorry if this sounds cynical, but after a life in and around the motor trade I have ceased to be surprised at the brass neck of some customers - On the other hand there are some, so called professionals, who thoroughly deserve it!