Work Orderless completion errors out from quantity being zero because we didn't use a BOM line

We have a BOM item that takes either a Hand gun (J-EPOXY-HCG) or Pneumatic gun (J-EPOXY-CG). Both are on the BOM and when a work order less completion happens we only want to use one of the guns. The transaction errors out from the quantity being zero for the line not used. Today there is no way to remove or add a component to the work order completion.  

Any thoughts on how to handle this Work Ordless completion? I tried BOM Substitutes where i removed one gun and made it a sub of the other, but appears substitutes are only for ASCP.