[fw-mvc] Using Action Helpers to disable the action dispatch

I'd like to bypass the action dispatch from within an Action Helper.
I'm using a customized ContextSwitch action helper to switch the
context of a request, and within a certain context, I don't need to
execute the action. I simply need for the Action Helper to execute
it's pre- and postDispatch functions (which set some view variables).

I've attempted to do this via the Action Helper's preDispatch() method
using $this->getRequest()->setDispatched(false). However, it's not
actually modifying the request within the Action Controller. I've
tried modifying the request, then setting the Action Controller's
request to the modified one. Still, no dice.

How would I go about this?

Thanks.