The Apple Studio Display required 24V and up to 1.87A, which I figured the iGo would handle well since it can be configured to output up to 70W and anywhere from 15 to 24V depending on the tip. The only thing left was how to trick the iGo into thinking it had one of the 24V tips plugged in.
Step 1: The iGo Connector
It appears that Pin 3 is the voltage limit, and Pin 4 is the current limit.
Pin 3 can have a resistance of anywhere from 2.5kΩ to infinity (open). 2.5kΩ sets the voltage to 24.5V and open is 15V. Any resistor in between can be chosen to get the desired voltage in that range. My 13.9kΩ tip tells the adapter to put out 16.6V for a Thinkpad laptop.
Pin 4 is a little harder to measure, since current limits require that you actually draw that much current. The tip had 162kΩ in it, which most likely corresponded to an amp or two. I actually found an article on Neripedia about someone else configuring an iGo adapter and he has the resistances listed that he measured from 9 tips that he has. The only discrepancy is that he lists the current limit resistances as voltage limit resistances and visa versa.