Not the cleanest way to do it, but you could use this conditional around the actual controls themselves.
Code:
<if condition="is_member_of($bbuserinfo, 6)">
<if condition="!$this->thread['open']">
(open/close button/bits here)
</if>
</if>
Embedded in the original conditional that only shows the mod controls to the proper usergroup in the first place.
So basically:
- If (it's you)
- If (the thread is not open)
- Show the controls
That way nobody will see the controls on closed threads but administrators.