I made that for the wife prior to getting a top box...........she still hasn't been on this bike. My bike is a Gen III and I used a tall back rest from a 1500 Vulcan Classic that I had left over. Used a torch to heat and bend the back rest to fit the angles and then welded on some plates to bolt the backrest to the same points that the rack attaches to. Painted it flat black and it seems to work well with my test sitting. It's now on the shelf since I purchased the OEM top case.I would buy something like that which was reasonably priced for a 1st gen in a heartbeat.
I'm sure something similar could be fabbed up for a Gen I also.