You could also write a console script, except that you don't want to type your password and reauthenticate once per follower. So doing it from the browser might be a better fit for a quick & dirty approach. This way your session would be reused.
Here's an educational bookmarklet. You can paste it in the URL bar of Firefox (didn't bother with other browsers) when you've opened twitter.com (won't work if window has a link open under another domain). And you can bookmark it- you thought it would be called a bookmarklet for nothing?
xmlhttp = new XMLHttpRequest();
for (i=0; i<list.length; i++)
+ query + "+from:" + list[i].screen_name)
This will open one search window per followee- so don't try this if you have loads of'em. You will hit a limit in Firefox' default config, and you can increase it using the property:
Still, you will hit a hardware/hardcoded limit if you're not careful with how many people you're following. I told you this only has educational value, right?