What's the best way to build JSON from a Forms instance?

For example, I want to pass many of the variable values (including tables) over to a stored proc for more extensive validation than it makes sense to try to do on the live form with lookups.

I'm currently building the JSON string manually with several [Assign Token Values] and [For Each Row]s, but it's kludgy and I have yet to figure out how to handle NULLs.

Is there a clean way to dump a form into JSON?