Editing a Custom Departure Point

I am trying to set up a departure point from a hold short position for any runway, instead of on the runway itself.  I can click on the hold short position on the map and set up a custom departure, but that starts me out in the air.  The altitude for this custom departure can be edited in the Nav Log to start me on the ground, but the speed apparently cannot.  Does anybody know if I can start at the hold short point?

Thanks,

Rush