Permit inbound calls of a certain length while blocking all others on Session Agent

Hello,

 

I'm looking to block inbound calls on a Session Agent that are NOT five digits long with a 404 response back. About the only thing I can come up with is this but I don't think it's going to work. Suggestions are appreciated!

 

sip-manipulation
        name                           PERMIT-5-REJECT-REST
        description                    PERMIT-5-DIGIT-CALLS-REJECT-EVERYTHING-ELSE
        split-headers                 
        join-headers                  
        header-rule
                name                           rejRURI
                header-name                    request-uri
                action                         manipulate
                comparison-type                pattern-rule
                msg-type                       request
                methods                        INVITE
                match-value                   
                new-value                     
                element-rule
                        name                           rejruri
                        parameter-name                
                        type                           uri-user
                        action                         reject
                        match-val-type                 any
                        comparison-type                pattern-rule
                        match-value                    ^(\d{5,5})$  (This captures Five digits, I would need one that matched on everything that is NOT five digits)
                        new-value                      404:Not Found