It turns out that if you remove the 4 rivets and disassemble the bridge removing the top aluminum plate and heatsink, you can install a Le Potato board with its heatsink. I removed the thermal pad and used thermal grease for the Le Potato heatsink and the bridge clears the heatsink with a small air gap. I was able to install Armbian Desktop and get it to boot. Now that I have it installed and booting I plan to run a stress test to see if it stays cool under load. I also plan to attempt porting the python code for the hub to see if I can get power down, battery status and brightness working (in that order).
I think (have not tried) that doing this will allow the Libre Computer Renegade to work also.
You do this same trick and flip the heatsink to cover more of the Tinkerboard S CPU but I found that still got pretty hot just booting up and would probably take a bit more work for adequate cooling.
For the bridge modification I cut and removed the four rivets. Once you do this you can remove the aluminum cover being careful not to scratch the PCB under it. The stock heatsink is attached to the aluminum cover with thermal tape and goes through a hole in the bridge PCB. If you are careful you could probably reuse the aluminum plate and attach it with screws to replace the rivets.
After checking again, the Renegade or Rock64 wouldn't work because they don't have two USB connections in the right spot for the trackpad/keyboard interface which uses two USB ports.
Now I just need to find something to load the CPU and monitor core temps and throttling so I can assess how well the stock Le Potato heatsink works with the bridge attached over it.
Was able to run stress on Armbian 5.56 for 5 hours to load CPU 100% with a max temp of 78C and the clock staying at 1.5Ghz (no throttling).
I have not stressed it yet but I have been able to get Libre's Ubuntu Bionic working off of eMMC.