Luckily, that will already be taken care of for most participants. Participant registration to the webinar through the form automatically lead to a user being created on Edgeryders and their registration being posted on their behalf in this thread.
We can very easily create another form that posts post-webinar evaluations and ideas. Anyone who is in the webinar without having registered through the form can then get their Edgeryders account by filling out that form instead - leaving all but their email address empty if they simply want to be kept in the loop.
It is very easy for us to them round up all those users and email them, or tag them in subsequent threads.