I’ve used the .stl file provided by @Avendor to make this expansion card for two full-sized Logitech unifying receivers.
I had to move the peg in the back a bit further back to make them fit, but it works perfectly. If I had any knowledge on how to work with 3D files, I would make it so that it printed in the proper position to begin with, but removing the peg with pliers and supergluing it into the proper location worked well too.
Additionally, I had to file down the plastic on the receivers so that the card would fit inside the expansion bay, but with those two slight modifications, everything fits and works perfectly.