This is possible on a couple of the assassinations.
The first is easiest, blend as soon as the cinematic ends and just stealth assassinate him while he is lecturing one of the merchants.
It is also possible to do this in the assassination of the doctor, the leader guy in Acre, the merchant king of Damascus and even Sibrand (the boat guy). You have to be pretty skilled but if you are really desperate just take your time and analyze the situation.
For the doctor for example there are all these drunks breaking your disguise but you can walk around them and wait for the doctor to come to a spot where they aren't walking.
ALSO very important. Use your memories pause menu. If you have done the investigations you will have the option(in some) to view additional information.THIS SHIT IS USEFUL!!! In the one with the scribe you can deduce his location from these info segments, in the one with the doctor it shows who his patients are and where he is going. Use these.