Open the skyspec.txt file in the skybank folder you are using.
Change this line to your values.
SunDirection = 100,100,100
Equates to
SunDirection = x,y,z position
But Not sure if this will change the shadows direction, I believe it just rotates the sky so you can line up your sun with the shadows.
This is still very much a WIP feature.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit