I wanted to do this too, even to the point of coding it myself. The data is easily exported from TR, top marks for making that available. TP even has an API that can be used to do the import (post payload-transformation): Workouts Create · TrainingPeaks/PartnersAPI Wiki · GitHub. TP does not make that API available to individuals however, only approved companies.
So keep the up-votes coming for this feature to generate the corporate will to get the lawyering done.