Step 1: buy a business card holder that looks just like a Famicom cartridge. Step 2: crack that card holder open. Step 3: put the guts of a cheap, emulator-capable media player inside.
http://lastchance.cc/gaming/nintendo/famicon-business-card-cases-131928.php%3C/a%3E%3C/p%3E
modder squeezes famicom into famicom cart (sort of) [technabob]