I guess for others trying this in the future with the S4M, I could see there is an option to use an ITX or Low Profile GPU and see if you can fit the HDPLEX 500W unit.
I can see @riba2233 forthcoming U-ITX case being a good fit for the this board. You could use a much more powerful GPU and have the 500W unit fit perfectly. You would still need to figure out the cables.