Hi,
As you said that, waste is not measurable in order to order.
This may be a one of the solution.
1. Create one order type without selection of BOM and routing.
2. Then create production order without material.
3. Add byeproduct material manualy in component material with -ve sign and qty.
4. Then do confirmation of production order ( GR of byeproduct material is with Mov. type 531)