Yes you can purchase discounted tickets at wide world of sports but they must be used that day or if you purchase a multiway pass you must begin to use it that day. There is a kiosk near the hub that can give you all the details. There may have been a half day pass too. I cannot recall the prices.
There should be a link with a code on your registration confirmation and you can purchase the tickets prior to your trip. Rundisney offers quite a good discount, but I do not remember the exact price.
There was no code or anything on my confirmation It just said that if I booked 4 nights and a ticket package I could get one marathon keepsake free.
I'm really disappointed that actual runners can't get some kind of discount on tickets for the park for that weekend. Kind of ridiculous actually.