If the B system is available, then why would you be using the alternate flap system? So the idea of switching off the engine driven pump to trigger the PTU to retract the LEDs under the guise of autoslat retraction would not be logical. Also, the autoslats work between "flaps not up" ans flap 15, ie when the LEDs are in the "extend" rather than "full extend" position, so trying to trigger the autoslat retraction logic would only return the slats to the mid position and do nothing to the Kruger flaps.
I also suspect more than a 10% increase in fuel burn with the LEDs extended.
As suggested, looking at the fuel consumption at 220kts and thus your endurance and then calculating range will tell you what alternates are viable. It just takes some basic arithmetic and doesn't need an FMC, though it'd save a bit of effort if the FMC had a feature to do this for you.