When using VP from an external program (Lightroom), it asks you to specify where the original RAW file is located. Although I understand it's not that easy to automatically find where this file is located, the user could provide some hints. Most of the time, the original RAW file is stored in the same folder as the file (TIFF or JPEG) passed to VP. So it would be easy to create an option allowing the user to specify that the original RAW file has to be searched in the same folder as the processed file. It will usually have the same name and the possible file extensions (CR2, NEF or whatever) could also be specified by the user as an option. Only if this search fails should VP ask for the actual file location.
It's easy and quick to code such a feature (can be done in less than an hour). Last year, someone at DxO Labs told be it was a good idea and that they were working at it. Nothing has changed since then.