different qty / um for replacement parts?

For Product Structures, we use replacements quite a bit (so far just Substitutes). For the primary part, we use for example: quantity=two, unit=feet for a spool of tubing.  In the replacement part, for this example, the tubing is precut to two feet, and is used as one each. In the replacement part UI, we do not see a field where we can select a different quantity or unit of measure. Is there a Windchill configuration that we can use to allow a replacement to have a different unit of measure and qty from the part that it replaces?