Workflow - bypass role

I have a promotion workflow that has static roles where three of the roles are sometimes not used for sign-off. I would like the workflow to just by-pass the role(s) if a user is not assigned, not have the workflow route through an alternate user.

I've checked and unchecked the 'Ignor unresolved role' but that hasn't made a difference.

Thanks in advance! Kathy

Windchill 9.1 M050 (test)