Item description Rule with non-mandatory EFF

We have below requirement from client and i am looking for work forward.

Requirement :-

when we enable item description rule , participating ALL EFF will become mandatory. client is looking for option to generate item description with MANDATORY + NON MANDATOY EFF's

For Example

Attr 1 + Attr 2 + Attr 3 + Attr 4 will be used for item description generation. whereas , "Attr 4" should remain optional field.