Some of the old signal switches I have salvaged came with a spring clip that snapped over the column and had a raised loop that held the wires to the column. Don't have any left now, even as a sample to take a picture. Probably never find any anyway.
What I plan to use on my current project is one of those aluminum or brass tie wraps where you stick the end thru the slot and bend over, should be able to pre-form a loop where it goes over the wires. Think it will better than a common zip tie.