Gamifying Lead Magnets

I've had a lead magnet (a "enter your email to download PDF guide") thing on a client's homepage for a while, and it does reasonably well. However, I wanted to add a gambling element to it, something like, "Click Here to get a free PDF guide" and RANDOMIZE it so every time it redirects to a different lead magnet. I'm guessing this would keep people on the site for longer and keep clicking on it until they've collected all 10 (or however many) PDFs there are.
How would one code something like this? I'm using Wordpress.