It's an avowed fake show.We have no idea how long they rehearsed the other "contestants" beyond what they say on what is a fictional show. It may not have been really a year.
I am sure they could have found someone to run Matt through all of the events for a couple of weeks before the actual shooting began. Much like attorneys run non-performer witnesses in "rehearsal" of what might happen in court. Over and over. So they lose their nervousness. Dr. Phil Mc Graw made a small forture (pre-Oprah) doing just that.
We see the show over a two and a half month period. The whole "shoot" was only about 10 days. Each day of shooting becomes a week of viewing.
I am sure he could have been run through the things that were going to happen to him in a location far away from where the rest of the cast was rehearsing.
Or maybe not.
Maybe he IS truly innocent.
That's what keeps me interested in watching this silly show to the end.