git bisect/checkout and changes to .gitignore

Greetings! I'm not certain if this list or the git-users group is more appropriate; my apologies if I've picked wrong.

At my workplace we use git to manage all of our source code. Every now and then, we decide that some particular file oughtn't to be git-managed, and add it into .gitignore and remove it from the repository (for instance, configuration files that become per-developer).

Is there a way to checkout an old version of the repository (before the file was added to .gitignore), then return to the current state, without destroying these sorts of files? Currently, checking out the old version quietly "takes control" of the file, and then checking out a newer one deletes it.

I've read through the man pages for 'git checkout' and 'gitignore' and searched the one for 'git config' (it's a little large to read all of), without seeing an option to preserve files on checkout. Is there a way to do this, and if so, where can I find it?

Thanks in advance!

Chris Angelico