Krybchynski,
I am not sure that a System Speed Dial will work for you as they do act differently even though they are both called speed dials. The station speed dial does not assume an outgoing digit and the system speed dial assumes an 8 by default for outgoing. The solution may work with a System Speed dial since you will have, hopefully, dial tone from the carrier after the hookflash, but I can not say for sure if it will try to grab a trunk, dial 8 or use ARS, before dialing. That is something you will have to test prior to implementing your solution. IF it does work then that makes you solution easier as you don't have to take up a station speed dial from each person to implement it.
Thanks,
TE