I'm pretty sure the prom chip inside that computer is not in a socket. However, that does not mean it's not possible to change the chip. The computer must be sent out and have a socket soldered onto the board. Special solder tools are needed to do this as if you try at home it could ruin the board. The problem is: if you apply too much heat to the board, paths will pull away. It may be a double-sided board which is even more difficult to work with.
My best advice to to call places like BMP or Dinan. Speak with someone directly so you can ask questions and get absalute answers. It might be no one makes a prom chip for that car because not enough demand. That still doesn't mean one is not available however. Typically, cars destined to America were detuned to run lean compaired to European specs. ECU's from Germany show up on ebay. Snag one and rock on. Probably be cheaper then having Dinan or whomever blow a one-off for you.
I had to at least dream about this for a while then pass. There's a turbo/diesel exhaust manifold on ebay right now. The guy says it will fit a 2.7 (325e) engine with little mods. The e engine is low compression which is right in a turbochargers path. The seller states the flange accepts a Garrett T3 (most likely a 40 trim compressor wheel) I was thinking small AR's for quick spoolup. This dream I was having included a compressor bypass, adjustable fuel pressure regulator, Lucas injectors, intercooler and a host of other nessassary items. When I started thinking about flaired fenders and 50 series rear tires I came back to earth. I'd better get the windows replaced first....