If the A/C circuit is 10 gauge and 30 amp as is required for the heater, then it wouldn't concern me to get the proper male plug and hook it to a suitable lead from the heater. Then just plug it in as you do the A/C. Probably not code and I'm not an electrician. But I did wire my own house when I built it and the inspector asked me if I did. I told him I did and he said he thought so. Because he said, a contractor usually doesn't do work that neatly!
It passed with no problems.