I did this before. It was pretty awesome, You had a map of each police station in a PDF with each parking slot numbered. Then in the config file, you had say:
[ HOVE BEACH ]
1 = Police
1L= 2
2 = Police2
2L = 3
3 = Police
if you left the L Livery blank, a random one would be made.
it worked across all police stations, and was really useful for adding a better role-playing Experience
Ill have another look, however I am incorporating a more efficient method of doing the same job in my new Metropolitan Police Mod