This option is not possible, @Roxanne Blackford. You may submit a Feature Request in our Ideas Portal at https://ideas.ringcentral.com/.
Actually Mary... ;)
You can create Call Queues with a single extension as a Member, and then change the Wait settings. Since RC is currently set up not to allow multiple calls going to the same extension when you're on an active Call Queue call, once you're on the phone, any other call to that 'extension' does not ring through.
The IVR would then have them send their 'extension' to the Call Queue, and once one call is engaged - all other calls would follow the Wait path.
Let me know if you want screen snips on how to do this.
Have fun.
Thanks for recommending this, @Joe Cache! I haven't tested this setup yet, but can we send the incoming calls to voicemail rather than waiting?