just a quick update: I've created a very bare bones python gui with two features:
1. menu option to open an archive file and extract it to a directory of your choice, displaying any output from the 7z command in a window
2. double click on the file in the file manager launches the gui and prompts you for the directory to extract to (you would be disgusted to learn how much time I spent trying to get this to work -- damn DBUS rpc calls!)

I'm still testing and will post new debs in a day or two. I'll create two packages: one with the gui and one with the command line tool (this time with rar support)