Well, it's Thursday morning now and I can tell you it worked for me. To see the different hunt groups do a "list hunt"
To determine available vector numbers do a "list vector".
In the above example I had no vectors so arbitrarily chose "10". I did a "chan(ge) vect(or)and set vector 10 as I stated above.
Then I did an "add VDN 2975" (2975 was the available number we decided to assign the vector). This is where you define which vector is assigned to the number, and I think you can override the group's COS and COR here as well.
It worked for my problem, which was to forward the calls to a 4 digit DN that wasn't defined (assigned) in the Avaya but was in the Infinity I wanted to forward the calls to at night. The PRI they would go to is an NI-2, but I don't know if it's classed as an internal or external span.
I haven't tried it with an "outside" number, but I'm going to bet it will work with that as well, maybe having to change the COS&COR depending on how your switch is programmed with respect to those call classes.