How can I permanently enable cheating?

While I wasn't able to get the .ini-based solution to work, there is another approach. Although billed as being for "earlier versions", the -hax0r switch works quite well with 1.112fm.

To add this switch to a Steam copy of the game, right-click it in your Library and select Properties from the menu. Click "Set launch options…" and type -hax0r into the text box. Click OK, then Close. From now on, when you launch the game via Steam, cheats will always be enabled.

If you're not using Steam, instead right-click on the shortcut you use to launch the game and select Properties. At the end of the Target box, add a space, then -hax0r. Click OK and you're done. Cheats will be enabled any time you launch the game via that shortcut.