Never have tried to put it into a parameter but I don't see why it could not be done to place onto the drawing. Usually we just supply dxf flat pattern drawing to our suppliers based off of information that they have given us. In order for pro/e to calculate a correct flat pattern you will need to know the bend deduct that you use with your bending machine. Then using the formula found HERE
to get the K-factor that you input into pro you will get an exact flat pattern. The key is to remember to use the flat pattern command and not unbend. Unbend does not take into account the stretching that occurs when bending.