Apparently yes, for yourself. Not for a third person.

The rules:

The Member's designated Companion must be an individual.. An individual may not travel as both a Member and a Companion on the same flight, except in Customer of Size instances...A Member who is a Customer of Size and earns a Companion Pass can use his/her Companion declaration for an extra seat.. To declare the extra seat as the Companion, the.Member must contact Customer Relations.