Mountainbear
If you have "allow redirect" checked, then simply program a button on his set to dial the number exactly how you dial it from the phone and include the route number to get a line. My office uses 9 so I would put the 9 in there. Then have them select the "forward" feature on the set followed by this button you just programmed as a speed dial.
You may want to add some restrictions to that set to avoid any calls out of the country or to a 900 number etc.
If you don't have routes setup for outside lines, and you are using line keys to dial, I suggest creating a route for 9 to use your lines or pool to dial. I am assuming you already have that.
Note: Feature *1 to program external speed dial
Note: Feature 4 call forward. If you do it this way, they press 2 buttons and done. Just program the speed dial with the route added. Simply try the number like this before forwarding so you know it works.
Hope this helps.
nooop