How can I enable the developer console on a non-US keyboard?

I tried to enable the developer console in the options menu in Portal 2, but it doesn't work out of the box because I'm using a German keyboard and the ~ key is not recognized.

I tried to edit the config.cfg and replace the keybinding from ` to \, but my changes are reset when I start Portal 2 again. How can I permanently change the keybinding for the developer console?

Do the following, just tested, steps:

1. Add the parameter -console to Launch Settings of Portal 2.
2. Launch Portal 2 (developer console should be already there).
3. Write and execute in console: bind f11 toggleconsole
4. Test that pressing F11 toggles the console.
5. Now exit Portal 2 and relaunch it. Everything should work as expected.