It is correct that the client does not currently have an easy interface to configure a follower. If you do want to configure it using the client you can use the advanced tab, it is a bit more complex than just setting the CAN ID. It requires the full CAN ID, and some specific configuration.
To set this up, connect to the follower device and set the following settings:
kFollowerID = 33888256 + CANID
CAN ID is the basic CAN ID from 1 - 62. For example, to have device 3 follow device 1, you would set this to 338882567
To have the device follow a SPARK MAX in the same direction set
kFollowerConfig = 436207616
To have the device follow the inverse of a SPARK MAX set
kFollowerConfig = 436469760
Check the configuration carefully and verify the operating direction before running with any kind of load.