Actually I just remembered something, there's a easy(?) yet cheaper way of dumping N64 carts. You can use a Gameshark 3.3's parallel port (it's on the back of the cartridge itself), plus some really basic software, to dump the game. They should be really common these days (friend of mine who wrote a guide about it only payed $8 bucks) on ebay. Maybe you can look into this first before I do something as drastic as asking someone to surrender their V64jr. :P

You can take a look at my friend's guide here:

http://ts.death.angel.googlepages.com/gamesharkstuff

I personally have never done it, but my friend has. Not sure if they work on prototypes, but I'll ask him when I see him.