I built nexus through my nexus install, downloaded all required jars. I then modified the attributes (C:\Development\Programs\Nexus\runtime\work\nexus\proxy\attributes\central\ant\ant\1.5.1\ant-1.5.1.jar && ant-1.5.1.pom.
After doing this, i noticed a couple of things. First the attributes were deleted, not moved to trash (which may be ok, just want to make sure the is the desired result). Secondly, the .sha1 files generated from the files in the attributes folder aren't removed when the attributes themselves are evicted. This causes the directories to not be deleted (in the proxy/attributes, dir in storage/blah is properly removed)