I was wondering whether you could use the Spartan idea to completely nail the one flank of an army while simply holding the rest back. I guess if you use units of spearmen on hold formation to just plain stop most of the army and then hit them with as much as you can on one flank (hopefully outnumber that flank 3 to 1 or something), it should crumble with enough time for you to get some units behind their army.