This can be achieved by a caller pressing * at any time while holding in a Call Queue. The caller would then be sent straight to the Destination if no answer set on that call queue once * is pressed.

It is worth noting this is not stated anywhere overtly, so if you want to make sure people know about this option you'll need to include it in your Intro Prompt or Hold Music.

Voicemail Destination

Most companies will want to set the Destination if no answer to a voicemail box, that way 

Loop IVR

Alternatively, you can us this to easily loop a queue for extra wait time with a break in between to check for voicemails.

Simply setup an IVR with the options Press 1 for Voicemail, Press 2 to Call Queue then set that as your Destination if no answer.

This does mean that when no one is available, pressing two will just repeat the prompt, so make sure your prompt acknowledges that in some way.