Hey Don, you doing subs only or are you doing MMA? Reason I ask is that I've found a quick way to break a Wrestler of that habit (aside from showing you can submit off your back), is to let them turtle up and box them around the ears a bit. Nothing too hard, just enough to show him another reason not to give up your back.
Other than that, a lot of drilling will need to be done to help "re-wire" his normal habits. Arm him with a set of sweeps and escapes first. Those will play into his wrestler mentality a lot easier than teaching him how to submit. Once he gets confident in his ability to get out from under his opponent, then start throwing in submissions from the bottom in bite-size portions. That way you aren't working against his wrestling background, but you'd be working an adjusted approach in conjunction to his wrestling background.
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