Well, you could remove bash entirely (say, by replacing it with a link to dash). Doing this will likely break things, however, up to and including rendering the machine unbootable depending on which distribution it is and how the init scripts are written.

You could replace bash with e.g. a perl script that strips parenthesis from your environment variables, and then invokes a differently named copy of bash. That might not break anything. Then again, it might.

I patched mine with a apt-get update sequence. It fixed the bug (first fix, not yet the second), and I didn't have to take the server down. Everything stayed up.