This doesn’t come up often, but it does come up. The only workaround that I can see is unsuspending, then unfollow, then re-suspend. Would make it much easier to just allow users to unfollow without the extra steps, or at least let admins unfollow for them… or have the ability to remove all follows for a suspended account.
Unsuspending and resuspending messes up the admin history on the account and so you have to re-document everything if you want a clean record (in case someone asks for a review of the suspension), so it is kind of a pain.