First I use git cvsimport to pull in the whole CVS tree:
git cvsimport -d :ext:user@host:/cvsroot -C myscript cvs_moduleThis will create a directory named myscript. Next, go into that directory and use git filter-branch to remove everything but the file(s) we care about (in this case, myscript again).
git filter-branch --prune-empty --tree-filter 'find -maxdepth 1 -type f \! -name myscript -delete' HEADThis ends up leaving some stale objects that can be cleaned up by removing everything other than master in .git/refs/heads/, the entire directory .git/refs/original/, and any unrelated tags in .git/refs/tags/ (at least in my example with no branches and such), then cleaning up with a few git commands:
git gc --aggressive
git repack -a -d
The total number of objects listed by git gc and git repack should be much smaller than the original number git cvsimport reported. (I also confirmed that git fsck --unreachable doesn't find anything.)
[Update] Apparently I had found this answer to my problem a while back and forgot about it. Oops.