It doesn't look like there's a feature for this, so it would require a little bit of custom code. I might look into it, but no guarantees. Modding Vichan's internals isn't very fun most of the time.
I believe NPFChan has this feature by default, or at the very least as a one-click install. Have you considered upgrading?
I was actually planning to upgrade to Lainchan's variant at some point.
You should upgrade to Cchan's premium software:)