Don't think there is anyway to have it reference the R3D. You could replace the loader in Fusion with the RED clip but you'd also need to reference the time code. My experience with R3Ds rendered from fusion directly was a nightmare due to small gamma shifts, it appeared the decoder in Resolve was not doing the same thing despite using the same settings (this may no longer be the case). I found Fusion connect to exr and back into Resolve was a solid workflow, I also think Fusion prefers exr over R3D.
Unfortunately you have to manually add the handles to the clip before you export, then once rendered you can trim them off again. I have found making a copy of the original and then disabling the original and sending the copy off to Fusion makes life easier for me, so you can still reference/revert to the original if need.