This article describes the loading of a bootstrap program into RAM purely by manipulating the timing of NMIs, on a Z80. The idea is that NMI pushes the current address onto the stack, and if you first fill memory with NOPs or similar, you can push any desired value. I'd like to understand this better and have a clearer description, but here's the doc:
http://www.jdm.homepage.dk/z80boot.htm
Edit: now found at http://www.z80.info/jmz8boot.htm

"Bootloading Z80 using NMI, RESET and CLOCK."

Cheers
Ed