What problem are you trying to solve? Does each customer get custom pricing? A different list of seminars to select from? What customization do you NEED on the web order form? Have you considered just putting the forms up with ugly generated URLs and assume that anyone who shows up must have received an offer?

If the pricing etc is different do the same thing but pre-generate ALL the pages with the customization already built in. That has the risk that someone will forward their e-mail to someone else, so you'd have to decide if you have the kind of customers who would do that.