Designate a special character sequence (such as "U") to initiate jumping directly to the bootcode

This is exactly the NoTouch approach, thanks.

As Andres is talking about not having a UART on the board, the "sequence" need not be "special". FlashMagic (for Philips) hammer, I believe "U" till it get a response, in Andres case (NO SERIAL USE by program) it can be much simpler: If FLIP hammers "U" as well just pick up the first "U", switch to ISP and the next (or third) will get responded to by the bootloader..

Erik