Follow can be mapped to a slot. To do it you need to type /slot (the slot number) /follow and press enter. The slot numbers are "Normal_____1 - 12
Ctrl________13 - 24
Alt ________25 - 36
Shift_______37 - 48". So on mine, to slot the /follow command to Shift+9, I type in "/slot 45 /follow" and hit enter.

On another note, I appear to have been wrong about HotKeyNet being able to send movement commands to the 2nd pc (healer). I made a change to my script last night and now the up,down,left, and right arrow keys control my 2nd character. In the Logitech G-key settings I created a macros that will hold down the back , left or right keys for 3 seconds. This proved very useful when fighting AOE enemies last night. Once the healer moves back though, I still have to hit the follow key to get him back in line after the battle.