This is another possible UI design for multiple attachment points and is a bit more visual though also more difficult to design implement.

Basically you would have an option like appearance in both the pie menu and also under Edit -> Attachments, this would switch your avatar to a "posing" position and open a number of small floater windows, along with a full-height inventory window to the right. The inventory window is much as normal, except that it does not display items that can't be attached; that is, it only displays objects and clothing items.

The floater windows correspond to different parts of your avatar's body, and have folders in them for each location, which will contain all items on that location. You can now simply add or remove attachments by dragging them to and from the individual folders within the floater windows.

Please refer to the attached mock-up file for a full-example