Okee, than we can make 1 gmapsupp.img with 1 FID. Even we can give the img a productnumber (010-12345-00 or something else. )
Next challenge is than to merge the 4 original sql databases with Activerouting-info to 1 database with the same productnumber as the *.img I guess.
I found some sites with info for merging sql(light) databases, but its rather complex and requires programming experience.
I give it a try