I'm trying to implement an available filter for an HTML portlet script. I'm not sure if this can be done since there's no GET/POST capability like with a Suitelet, only the render entry point. Is this possible?

I think that once I added a suitelet through an iframe into a portlet to achieve something like that. I do not remember exactly what I did.

Ya, I was in the process of creating a suitelet. Those portlet script types are really restrictive.