Glad to see someone bringing up this topic.
I have an FFC cable on one project of mine, where I'm still looking for a better way of handling insertion. In my case, it goes around a bend (display on one side of the PCB, connector on the other).
I found that using a combination of my fingers and a plastic spudger-like tool definitely helped with inserting the cable into the connector.
However, I still wish I had some sort of tool that helped with actually closing the connector. The problem is that I kinda want special pliers that can squeeze both sides of it at once, without touching the middle.
Do special purpose tools for dealing with all these FFC assembly issues even exist? I haven't seen them mentioned anywhere, and you really don't need them for a one-off project, but there has to be something used by people who assemble products with these cables all day long.