How do you merge an active call with a parked call?

Hi All,

I have been saddled with the absolutely maddening issue with RingCentral that any call I place on hold starts ringing like a new call on my assistant's phone who monitors my lines.  As a solution I created parked call presence locations on my personal phone so I can place someone in a parked location and my assistant will not see the call as a new call on her line.

I need to figure out a way that solves the following scenario:

1.  I am on an active call.
2.  Another call comes in while I am on that call.
3.  I place my current active call in a parked location so that it is on hold without my assistant seeing it ring like a new call on her line.
4.  I answer the new incoming call.
5.  The person on the new active call is someone I want to join in a three way call with the person in the parked location.

How do I complete step 5?  

If I hit the conference key on the phone and hit the parked line soft key, the system tells me the parked location is no longer available.

Likewise, if I am on a single active call and want to add another person to the call and I hit the conference key on the phone, Ring Central immediately places the active call in to a "hold" status (causing it to ring on my assistant's phone as if it were a new call) while I dial the third person I had been hoping to join on the line.  By the time the third person answers, my assistant has already answered the original call thinking it was a new caller.  

Thanks,

Jeff