There is no rights based administration system in Openfire. Every admin has full rights. I think there is a ticket for this in the bug tracker, but this is a very complex task to do.
calebtr, this will only work if client is not using its own broadcasting feature. Spark is not using Openfire's broadcast plugin to send its broadcasts. It just sends many simple messages. So the only thing to forbid that is by using Client Control plugin and disable broadcasts in Spark. But in this case noone will be able to send broadcasts in Spark.