A student of mine was 6'2 350lbs and wanted to get his Private in the 172SP. With me at 6' and 200lbs, I told him his options: (1) Fly the 182 or (2) Find an instructor that weighs 120lbs. He went with option #2.

It's not worth flying an overweight airplane by exceeding the limitations and breaking the rules. You need to set an example as a CFI.