Converting from Theatrical to High Deffinition

I recently finished grading a film for theatrical, monitoring in DCI-P3 colorspace on my Dreamcolor (I know now that I should have monitored in Rec 709 and converted after the fact). Now I need to do a trim pass for the HD delivery to BD and DVD. I have been trying to find a LUT that converts from DCI-P3 to Rec 709 but without any luck. I noticed Resolve 12.5 now has a X'Y'Z' to Rec 709 LUT, but I did not grade in X'Y'Z'.

Has anybody used a LUT that converts DCI-P3 to Rec 709?

Andreas