Configure extra target with StarWind, use initiator to map it as a raw disk device and... iSCSI part stops here. Next goes generic Windows DMIO thing. Key words are "dynamic disk", "spanning volume" and "NTFS". Nice place to start and read about initial limitations is here:
http://support.microsoft.com/kb/225551 and again, Google a bit as topic has very little in common with iSCSI in general.
P.S. Replace "DMIO" with "LVM", "Windows" with "Linux" and "NTFS" with "EXT3FS" and you have pretty much the same picture on Linux.