Is there a way for Voix Manager to show an extension as Available, even though the handset is unplugged?

I have several extensions that are permanently forwarded to outside numbers, and I want the receptionist to be able to transfer incoming calls to these extensions. However, if I disconnect the handsets, Voix Manager considers these extensions unavailable, even though they are active and working in Asterisk.

I just don't have the desk space for the extra, unused handsets.