just my 2c on this. I know there are a few of you that are electronically minded. who says you have to clone the chip directly? fire it up get it to spit out serial data and note that down. if if you are really intrigued and feel like memory mapping it then you can work out HOW/where it writes things to and write your own code for it.
the ONLY catch to this will be if nissan actually forgot to lock the thing. given that its nissan I would say the didn't and the hitachi's internal flash has been locked down. you will have buckleys of getting unlocked.
I know a certian russian fellow that worked with hitachi SH4s so he could probably tell you a thing or two about them - food for thought.