Workflow-problem: Rating with JPGs, adding RAW later

Hi,
I shoot with RAW + JPG.
The JPGs are for quick wireless transfer to the PC during the shoot.
Already during the shoot I want to use FRV to view, check and rate the photos (the JPGs) and sometimes write titles and comments.
These added EXIF infos are saved to XMP sidecar files.

After the shoot I want to copy the missing RAWs to the PC and then do further rating/culling.

But this happened:
When I relaunch FRV my EXIF editings are **not** displayed. It seems as if I have never viewed and rated the pictures before. It may even be that browsing through the pictures will generate a new XMP file and overwrite the existing ones with the saved ratings and comments.

I looked into the xmp files with a text editor and found that one difference was:
The old ones had a statement in the content that they belong to a "JPG" file whilst the new ones stated "ORF" (parameter = "<photoshop:SidecarForExtension>").

As a workaround, now I take my text editor and use the feature "find and replace text within multiple files" to globally replace the above mentioned "<photoshop:SidecarForExtension>" from JPG to ORF. I do this before I copy the missing RAWs into the directory on the PC. When I then open FRV all my former ratings and comments are preserved and correctly displayed. I can then browse through the pictures and do further rating and culling.

This workaround is - although it does the job - an extra step and - because it is a manual procedure - you have to be very carefull and may even risk to introduce errors or render the sidecar files unusable. Therefor my question is:

Is there a better way to transfer the JPG ratings to the RAW photos?

Thanks in advance!
Ralf