I think he wants to have a killswitch for running tasks on the taskbar in a skin something like this 
 

The grey button to close for example when you mouseover, but you could also do a right click to close these... 
But i guess that is something that could be integraded in a future WB release... 

Hardly you would "achieve" by registry or through Stardock apps. It's one unique functionality that you have to seeking for third party apps/plugins to satisfaction.  

No i made it to explain what was requested...since most folks here are skinners and not developers your request is directed at the wrong source.

If you want such a function it would be best to contact Stardock support an make a enquiry for it ( if it would be possible to integrade such a function into a future release ) 

*However a killswitch is to terminate a not responding/feedback program (can be done via cmd/Taskmanager) that command must be directed at a button, a button that is is not existing ... yet
Another option would be the more simple close active app...  
You asked if this can be done by tweaking registry, i would recommend to keep distance to such
a approach on your own *  no offense but altering registry is always the last choice and would not help since it needs to be pointed to the button.
I shutup now and beg you to just write a email to support.

Currently it is weekend and support will be available again on Monday but you can always write a ticket in advance but you will have to be pationed.

If you are lucky a Mod might see this Topic and call it to attention of a Stardock Developer/Employee