I would also strongly suggest that you start training your heavier paddlers to paddle on boat sides. Last year my team had two paddlers over 245 pounds. Unfortunetly they both paddled stronger on the right and tired out quickly if I moved them to the left. That meant that I had to put some paddlers on thier weaker side to balance the boat. If both paddlers were on the right side that meant I had to figure out how to off-set the 490 pounds with only two people in the boat.
Have to agree that both sided paddlers give more flexibility in setting crews. Also, if they do both mixed and single-gender racing in the same festival, you can have them do one side for mixed and the other side for single-gender.
But in the situation described above with two 245 pound right-side paddlers does have a possible solution if the festival has 11 seat boats. Put 11 paddlers on the left side and 9 on the right side.