If it is an invitation to a seminar, sell the knowledge to be gained at the seminar and not the product being promoted. A lead generating package should never sell just the product. It should also push the offer. And there is always an offer. The best offer is some type of free trail, free analysis, free consultation, or free sample.
Premiums can also work well.
Free information is an offer and it does work. Write copy that enhances the perceived value of your offer. A product catalog becomes a product guide. A software catalog becomes an international software directory. A collection of brochures becomes a free information kit.