Please Note: This trick is for automatic printers , but might be something you could do manually if your willing to cut some special squeegees.
Many years ago , when I was still a printer running an automatic at a very good friends shop, he got a huge order for these youth design shirts that had a bunch of stick figures in 10 colors. The press I was on only had 8 heads (7 with a flash) and at first my friend was going to turn the job down because it was simply too many colors....but as I looked at the art, an idea stuck me that the design lent itself to being separated in a way that allowed it to be turned into a 6 screen job. And that is exactly what we did...as you can see below some of the colors only printed on one side of the shirt. So I constructed some cardboard dividers and used Polyken tape (very sticky) to tape them. I then built some special squeegees with a divider in the middle and used the smallest (4") floodbars we had to ultimately do 10 colors with only 6 screens and NO FLASH!