How to import metadata from extermal .xmp sidecar file when importing .jpg files into Lightroom?

I have thousands of image files that I want to import into Lightroom. Some of the files are .nef, some are .jpg, .tiff, and other formats.

If I have file1.nef and also have file1.xmp in the same directory, when I import file1.nef it automatically brings in the data from the file1.xmp sidecar. But if I have file2.jpg and also file2.xmp in the same directory, when I import file2.xmp it does not bring in the metadata in file2.xmp. I believe this is because Lightroom knows that certain formats such as .jpg can contain their own metadata, so it looks in the file instead of looking for a sidecar.

Is there any way (perhaps a setting at import time or a general Lightroom setting) to force it to take metadata from file2.xmp when I import file2.jpg (either as the only metadata or as additional metadata beyond whatever metadata is in file2.jpg, either way being okay with me)?

UPDATE: In the meantime since asking this question I found: http://www.codeproject.com/Articles/43266/Reading-and-Writing-Photo-Metadata-Programmaticall

and I am now writing the metadata into my .png and .tiff files.

But it would still be nice to know if I didn't have to do this.