I'm not aware of a method. Perhaps there is, perhaps not.
But from your post, it sounds like you bought a product that uses a Teensy to do a project, but you are balking at paying the developer for more boards. Instead, you want to clone the board, and not pay the developer anything further. I imagine in many of the places that use Teensys in their product, they can't just depend on the sales of just one board to fund the entire process, but instead of spreading the cost of development over many boards being sold.
If you think somebody is charging too high of a price, don't buy a board from them with the intention of ripping them off. Instead create your own version (or hire somebody to do it). Then you can decide whether to sell your version at a lower price, or make the software freely available.