Panels and Webform, how to send arguments

I've recently installed Panels. I think is an awesome module.
I've been using webforms as blocks in nodes. One of them is a forward.module like webform that gathers some extra data. I was using a hidden field with a default value of the current URL. That worked.
What I want now is the Panel to pass the Nid to the webform and capture this value somehow, either with a hidden field, or some php in the template or with the webform post processing php that I'm using to send the e-mail.

Any advice?