A while back I updated sebastienj's Fileset Attribute add-on for 5.7, it was really just a case of adding a few namespace lines so it didn't take long.

I did ask Sébastien if he wanted a copy of what I did to push up to the marketplace, but I didn't receive a reply.

I've attached a zip of the 5.7 version. As the 5.6 is free, and there's basically no other way to code this, I'd be surprised if Sébastien has any problem with me do this - but I'll remove it if I'm wrong about that, don't want to cause any issues.

Just unzip it into the /packages directory and install via the dashboard.