Two ways I have seen this done, and keep the ignition switch:
1. Remove the switch, cut a section of beer or soda can and wrap it around the column, resinstall the switch. Keeps the lock from going into the hole.
2. Remove the switch, retract the lock, drill 1/8" hole through the whole thing. Drive a 1/8" roll pin through the whole deal. Now it won't move.

I have seen the first used on many cars I have worked on, I have the second on my car.

I was following a lady in the first race of my first school at Lowes Motor Speedway in the early '90's and she lost it going into #1 and hit the tires. She ended up on her side with the roof facing traffic. Fuel pump was still running, but the driver had temporarily shut down. The battery sparked and ignited the fuel and started a fire. The Corner workers couldn't find the shut off, as the ignition had been removed. I finally reached in and shut it off since I had a full suit, gloves, and helmet still on. But remember, this is all prior to mandatory cutoff switches. Caused me to install one several years before they became mandatory, cells too!

Mike