I diid some searching and I only found a couple threads about doing this, the end result of pretty much all of them being the recommendation to use a gamecube controller. So I decided to make this thread on how I padhacked my Classic Controller.
The classic controller is a common ground.
Unforunatley I didn't take pitures during the process. But here's the PCB with the solder points I used. You'll have to scrape off the black stuff to expose copper to solder to. Ignore the Red markings.
And here's my completed mod. I was able to get everything jammed back into the classic controller and the actual buttons still work. I chose not to connect anything to Start, Select or Home cause not enough buttons on my HSS-0130.
It's a DB15 cable attached so I can hook it up to my HSS-0130.