[Blaiz889]

Funny!! Sounds pretty close to what my gelding would do. Note: It took me and my trainer a few months to get him stretching down and into the contact.
What would you do if you were this rider? I wouldn't mess around with side-reins, ground driving, ect.. The problem is obviously something to do with the rider. Since he is an OTTB, he is not used to riding with a steady contact, stretching to the bit, and using his back. Getting him into a nice frame and working into the bit comes from forward energy, soft hands, and a round back. It will take time to stregthen his muscles. But, moving onto the contact issue.
A "small bit" on keeping a good contact: You drive your horse up into the contact using your legs and half-halt with your seat and outside rein, while keeping contact on the inside, to collect, control, and round your horse and their stride.
A soft hand means steady elbows that relax and bend so that your lower arm and hand can stay in one place. Then you don't 'bump' your horse in their mouth. Soft hands means a steady contact. To keep the horse from pulling and leaning into the bit, and to keep the contact playing, I "wiggle" my ring fingers. Just kind of massage the reins with them. Pretend you are holding the reins. Your thumb is on top, your three middle fingers are closed, and your pinky, kinda curled but out more. When I say wiggle I mean, press your ring-finger into your palm on and off really quick, alternating hands.
Ride him into a contact. Use your leg and seat. Keep playing with the reins and keeping the contact light.
What might be a reason for this evasion? I agree with TBnut. He just needs patience, and repitition.
What can the rider do to help? Same as above.