For those interested in getting the keyless entry part of the system and can't find MTI's solution here is what I bought and installed in my w124.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=8018233912
The installation went relatively smoothly and I used a dremel tool to get the key cut to the right shape and cut the groove for the screw to hold the key in place. I didn't even have to use JB weld as the screw mechanism worked as it does in the other OEM MB flip keys and holds the key securely.
I bought the unit on the german ebay (ebay.de) from the same seller and paid about $20 (USD) less than the buy it now + shipping no the US ebay.
I love having the flip key AND the keyless entry.