David,
There is no Out of the Box Configuration Option to send a message to all agents of a group.
From my research Administrators within the contact center shall have the ability to broadcast messages to all agents logged in. You have to add customization to send and receive broadcast message. IWS and WDE are a T-Lib client. It is my understanding that sending a request is pretty simple, but we'll still need to build an IWS or WDE module or custom GUI around that and integrate it into the IWS or WDE. This custom client would send RequestDistributeUserEvent with attached data in the specific format to the communication DN.
http://docs.genesys.com/Documentation/IW/latest/Dep/ViewingBroadcastMessages. Therefore this requirement would be customization. GA for the communication DN setup and Custom for designing and implementing the custom client that would send RequestDistributeUserEvent.
Regards,
BIll D