P5v2 had it right. A widget that allowed you to name the editor and point out the file path. It could be in the preferences menu.

There are two ways to get third party editors into the SONAR tool bar https://www.cakewalk.com/Support/Knowledge-Base/2007013099/Adding-third-party-audio-editing-software-to-SONARs-Tools-menu or use Duckbar http://www.sonarmods.com/forum/index.php (register to download). Duckbar provides a graphical interface for the needed registry entries. If you are concerned that Duckbar may change SONAR in some way, it does not. Adding Duckbar to your installation does not modify SONAR in any way unless you choose to do so. Duckbar can be used for the registry tools interface and other config changes without affecting the SONAR program itself. Duckbar may the easy solution for now.

Thanks scook! - I remember dannyd once talking about a utility that did the job- it must have been duckbar. 
The Cakewalk method sounds too much like hard work :)

You may be thinking of SONAR Utils. It was a popular utility a few years ago. It had a graphical interface to add editors. Unfortunately SONAR Utils does not work with 64bit SONAR. Duckbar is a relatively new utility for use with X series SONAR. It provides much more than a simple interface to the Tools Menu and config options such as extensive color customization, a staff view notes menu, toggles for parts of the interface and picture cache management.

The long involved process of adding a third party editor is a bit of a pita,, but you only need do it once after every re make of your system. I would like a short cut too, but I think I'd rather vote for better Sonar wave editing tools so we wouldn't need the 3rd party.. 
 

finally got around to writing a utility to make this process easier, info about it is here http://forum.cakewalk.com/FindPost/3237117