Bill, that is elegant !!

Then in the external eprom have some code that sets the ENBOOT bit (in AUXR1, I think). This makes the bootcode visable to your code. Then do a JMP to FC00h this will take you to the bootloader.

NoTouch does just that and require thus no "funny signal levels".
"The backdoor" a means of doing the same in a way that almost mimic the 'V': If Txd is held low at reset the chip enter boot.

NoTouch is intended for customer updates, "the backdoor" is intended for development.

Erik