Check out the submodule into a subfolder, for example /foo/submodule
, so it looks like this:
/foo/submodule/foo/bar/file.text
/foo/submodule/foo/one/otherfile.txt
Then simply link the files in your repo:
/foo/bar/file.txt --> link to ../submodule/foo/bar/file.txt
/foo/one/otherfile.txt --> link to ../submodule/foo/one/otherfile.txt
This could even be expanded to automatically update the links and remove dead links when you update the submodule by a git hook if necessary.