Message to participants just before or at meeting entry - without presence of the host

Is it possible to set up waiting room a few minutes before entering the Zoom, without interference by the host?

I want participants to be able to meet without a host, and I need them to see a message with some instructions before they actually enter the meeting.

They register through another program, so their email is not known by Zoom. 

Ideally I would use a auto-respons in the chat, but I found that that option does not exist. Hence this question. 

Many thanks!

Andrina