It's mentioned in several places in the help and sample code that you can redirect to a second assistant from a primary assistant.  In the code sample they are using an HTML link to jump to the other assistant but in my setup I'm redirecting in a POST event.

Basically, if a user checks a certain option when they navigate to the next step I am redirecting them to the "sub assistant" and then upon completion I want them redirected back to the original, the latter of which should be handled by the customwhence property.  Problem is, when my assistant is finished it just redirects to the regular finished step rather than going back to the original assistant.