Did it ages ago when the Warmaster fantasy rules came out and the figures weren’t yet available.
Did it recently when Chain of Command came out and we had some unpainted figures but none of us had vehicles yet. Assuming things like a box that had contained a few overpriced chocolates with a straw pushed into the front and the inscription StuGIII in marker pen on the top counts as paper armies. It did rather well, that StuG (supported by the Wehrmacht’s finest space marines) in cutting down the Soviet Union’s pesky Space Elf Strelky. 🙂
Growing old is mandatory, growing up is entirely optional!