Modifying "cool only" Coleman Plenum 8330B751

I am trying to add heat strips to my a/c units. I had the heat strips on order and decided to confirm with RVComfort I had the correct set-up; yes and no. As it turns out, I do not have the correct plenum controller mine are for "cool-only" and I need to replace them with essentially the same exact thing 8330C5091. If I understand correctly, these are the same controllers, except they did not put in the relay for the heat strip off the controller board. This new controller is 150-180usd.

Has anyone modified their "cool-only" to add the missing relay, save the upto two-hundred bucks per controller?

Thanks,

~David