I came up with complicated and far from pefrect workaround:
Since we’re not able to create a sidecar XMP file, I created a very small quicktime animation clip (1 frame, 16×16 px black background) which can hold metadata just fine. I then rename my mov to the same name as original file I can’t edit (or just add something like _bridge keywords_) and check all the needed keywords. This way the two files are always displayed next to each other and when I search for a specific keywords I get a pretty accurate result.
This is not a final solution to the problem, since you still have to manually select the original file (search only finds the black little movs).
Hope that helps for now,
good luck!