I don't have a device to use as a tiller so I have not tried this, but there are possibly a few ways.

If you have FSUIPC, this program is capable of assigning a tiller axis, however I do not know if it will function the same as the one built into the CS 757.

If you don't have FSUIPC you could try SPAD.next (payware, has a graphical interface) or LINDA (free, but basically a text editor for scripting commands in LUA) to program the tiller. Read the CS 757 SDK in the manual. There are instructions on how to program the built in functions which includes the tiller. See the LR.JPG file.

I believe the tiller is variable L14_001_LVR which would be converted into a number 2214001

I'm guessing they have it used as a knob.

If it was a knob you would have to set the LVAR "KLID" = to 2214001 for clockwise and -2214001 for counterclockwise.

Unfortunately it's not the most intuitive. I managed to get all the autopilot commands to work on my Saitek multipanel after a few hours of tinkering, so it does work with some trial and error.