I've been championing this one but I was misguided. It could be even simpler.
 
Make it so:
 
We can right click on an inserted effect in the effects bin (or otherwise) and "Send it To" a layout / layout folder via a browse dialog for an existing plugin layout.
 
Furthermore, have Sonar maintain a list of new plugin the background scanner found for the duration of the launch that found them (like the FireFox recent downloads) so we can quickly pick them to try them as we just installed them if we so choose.