Abillity to link to existing css-file instead of making a new

My situation was that I had all the css-tags I wanted to add in one css-file, so I had to copy the contents into the textfield instead of just using the existing file.
I would like to be able to give the relative adress to the the file and use that one instead of generating som generic file called css_injector_X.css.
Would that be possible?

This way it would be possible to separate the css-files from eachother by be able to recognising the files content by its name.

Ps. some integration with upload.module would be in the same neighbourhood, but that would not be my favorite way to do it.