Comment 6 for bug 786191

Experimenting with bug 1002602, I found a workaround for this.

If you don't need the decoation bar:

Set "Decoration Windows" to "none"

Leave other settings as they are.

The window menu (alt+right click or space) will be available.

Windows will also have shadows for borders.

If you don't need shadows or any kind of border:

Adjust the settings for "Active/Inactive Shadow"

Leave "Shadow windows" set to "any"

Without this, the decorator will not run, ergo no window menu.