Don't want to take you out of what your program is telling you to do, but the way I see it is that you layer whistle commands just like you "layer" any aversives. And if it were me, I'd get either a 30ft. checkcord on the dog with a choker or just a c.cord by itself and from a remote, command HERE, hit the whistle and use the checkcord to get him moving. Once the dog "gets that", then I'd make the collar a "replacement" for the checkcord, but not until the dog begins to move upon the whistle every time without the verbal. Incorporate the *nick with the checkcord.
You don't use the collar to teach- you re-enforce with it.
Swampbilly1980- I got a feeva',..and the only cure is more Mergansers and face paint.