Posted there, but basically, you need to set your efficiency at whatever it normally is, then divide the gravity points up.
I doubt you get 90% efficiency on your system!
If you get 75% on average, set one up for 45% and the other for 30%. Easiest way to do it once you have the recipe is to get your preboil volume on the first brew, step back, check the gravity, do the math to get the gravity where you want by pulling some out and topping with water, then finish running off into the second one.
This is a great time to have some DME handy, BTW. These sorts of things rarely come off like they're "supposed" to.