We fear that we would get lots of support tickets about this feature if you were not a UK user. Anything which is country specific or continent specific might cause us issues with other customers for other areas.
Just a thought, but if you're concerned about support tickets, then you could implement this with a very basic set of codes allocated - for example:
0000 - 7477 Air Traffic Control
7500 Special Purpose Code - Hi-Jacking
7501 - 7577 Air Traffic Control
7600 Special Purpose Code - Radio Failure
7601 - 7677 Air Traffic Control
7700 Special Purpose Code - Emergency
7701 - 7777 Air Traffic Control
And then allow users to develop their own list of local squawk codes, much like we do for airline logos, country flags, etc.