I'm not sure if this is even possible,

I have a user group who is prevented from sending emails outside of our GroupWise system (i.e. they cannot send to internet addresses). I have a new requirement to allow this user group to send and receive email to a vendor who will be onsite with us for the better part of a year, however the group must continue being prevented from sending email to any other external addresses. Is this possible with GroupWise 8, or am I stuck with creating a 'forwarding' user in GroupWise (with all the associated nightmares that is going to be) to allow that user group to send to this vendor. The vendor cannot use a GroupWise account that could be created for reasons they choose not to make me aware of, which would have been my other work around for this.

Thanks in advance,