Technically, there is no stipulation for a straight six in the Guest Artist Contract.
This would need to be brought up to AEA - given he is the only person, and he is asking for it - I doubt the union would not grant this concession - but technically, no . . . a straight six is not listed as an option.
I don't the history of this contract, but technically your Executive Director is right; this contract does not allow it with the rules as written.