I've only built and operated an RX-1 and a YG4i on both snowmobiles, F1000 cars and aircraft, so my experience may severely wanting (sarc). If you already know the answers, why are you asking questions of us already well familiar with the powerplant here?
If there was a way to achieve a solution without an external PSRU on this plant, believe me it would have been done. Many of us here may be incredibly credentialed & experienced mechanics and engineers (like myself and many others), but that doesn't mean we go all out to make things unnecessarily complicated. If there is a simple way that works, we gravitate toward it- no need to reinvent the wheel at expense if the solution already exists.
But if you have the answers, go for it, and show us your achievement... in fact I encourage it.
Mohawk Aero, SkyTmy freightliner swmi teuck was designed by great engineers rax, Rotax-C for the RX-1/YG4-YG4i. As the Mandalorian says, This is the Way.