you can re-number files as you import
you may need to a test of a few un-important files
click the re-name file panel >>tick>>template>>click on arrows>>edit and that will take you the customize panel
add image name like "img"
then add numbering I have only used the first one (import)
make sure you add two "00" so they stay in order
should look like img-001
bugga of a number tool imo; bridge is easier/better
you could also rename in windows or bridge or other programs before importing BUT ONLY IF THE FILES HAVE NOT BEEN IN LR ALREADY. Sorry to yell thats important as you most likely know
Yell if that doesn't make sense
After importing, you can copy filename into another metadata field in Lightroom, would that suffice? - i.e. the filename would not be in exif-metadata (in the photo source file), but would be available in Lightroom and for exporting as IPTC field for example.
There are scripts and/or plugins that would help.. - let me know...