It would take some custom machining but is the M48 threaded camera side of the reducer removable with a locking ring behind it that retains the glass elements inside the reducer? I am assuming you have one of the QHY OAG assemblies where you can bolt it direct to the front of the camera or filter wheel, and/or bolt on adapter plates to fit it to everything else?
If that was the case and the diameters of the fixing screws and thread of the reducer housing were suitable you could get an adapter plate made which bolted to the OAG on one side and screwed in to the female threads in the reducer in the other.
I assume you have this reducer?
https://www.astronomyalive.com.au/pr...cer-flattener/