How to return data from a callback function? (form validation)

[eluser]stormbytes[/eluser]
Exactly correct. I'm trying to return a value (var, array, etc) from the validation callback function. I'm wondering if this is possible? The user guide seems to imply that it is.

I've already tried using flashdata (session) to pass my array to the validation function (controller method that receives the validated data) but for some reason the flashdata is purged as soon as another model is called. Weird.. It's supposed to last through the http request.