Oh I had another idea:
Pay for some sort of graphical flare or other show-off trait for your army. For instance, Perhaps your troops gain some sort of elemental war-cry that flashes lightning at the beginning of the battle. Or perhaps an effect that makes the map/ground look cracked after your army marches over it (and dissapears soon after), etc. These would do nothing but look cool, mind you.
"He uttered the word of curse, crush him with our Orcish iron!"