You might be able to do it actually. If you go into the category you created for PAID files, there is an option to add group permissions. Not sure, but if you created a custom group you can move Mates into and add that group to paid file category with the option ticked to download the paid files.
No idea if that works (untested). I suspect all that does is either deny or allow a user or group to download paid files, anjd won't make any difference letting them download for free. But try it and see
Or even try just entering his mates name in there (no group needed to be added) then and see if that works
I actually had tried that but it didn't provide a download link, just the buy link still.
Creating another category just for the member is was my next step but figured I'd post here in case I missed something.