In workflow, check if property has more than 1 entry

I'm creating a workflow.  The first two states are Draft and Reviewer(s).  The Reviewer(s) property is multi-select.  I require the user of the workflow to enter at least two Reviewer(s).   I set the property pre-condition to check if Reviewer(s) > 1.  However, this doesn't seem to work.  I guess the ">" operator is used for numbers only, and not quantity.

Is there a way to accomplish this without creating two different properties?