You do not need to do 100 unique services to get this. The tracker does not work so you’ll have to keep track yourself, but it does work to repeat the same service over and over. The shortest service I found is with the Gallery Cab Car, the 282F Empty to Depot option. If you go full speed ignoring speed limits you can complete it in about 2 minutes. Then just Replay Service at the end and repeat as many times as you need.
Note that this is not the most efficient way to get the other achievements for this DLC and will leave you well short on XP for getting to level 20, and won’t get you any distance toward the 400 miles with the F40PH, so I would only recommend using this to fill in when you’re at or near the end of those other achievements.