most flight attendants in the cockpit would take a little more reassurance than you telling them not to let the captain in.
I've asked three flight attendants to open the door when the F/O was ready to come back in. Not one of them could do it. 100% fail rate of the new system. I'll keep asking but I don't think the stats will improve until the new procedure requires training of the flight attendants.
This says quite a lot about the implementation of the new procedure, and the motivation for it's existence.