Printing multiple prints stacked on top of each other
If you can get it to work reliably and with decent quality, it would be a good solution. However, you might find it unreliable and the bottom surfaces of the objects might not turn out very nice (as is usually the case with overhangs that needs support). How well this will work is strongly dependent on the object being printed, and this probably will only work for a very small class of objects.

You don't gain much by doing this, as printing multiples "at once" isn't much faster compared to printing them sequentially (that is, if you have time to check on your printer and reset it between prints).