Might be difficult to adapt a hack to a Gt. On most sidecar rigs it's necessary to change the fork rake to make the set up steer unless you're an Olympic weightlifter. It's not as easy as making mounts on the frame to link up to the scooter. There will be considerable more wear on the drive belt, clutch and brakes on the bike due to the extra load.
I've seen a couple trailer setups made for dogs that work well. One guy around here had a Goldwing with a trailer he built for his dog. On rides with a him and a group it was fun to watch the dog, a black lab, when we stopped for a break. He'd go around and greet each rider and sniff the bikes and bum munchies. His owner carried water for him. When we all started putting on helmets the dog jumped into the trailer and barked until his owner shut the mesh door. There was a hole with a soft rubber rim where he could stick his head up through the top.
Something like that would work if one could come up with a trailer hitch for the scooter. It would still be a bit of a load increase on the bike and its components but as long as the combined weight didn't exceed the bike's maximum weight it shouldn't be dangerous. At least it wouldn't change the scooter's handling characteristics much.
