Unfortunately there is no way of doing this through the web console, that I am aware of. The way we've dealt with this is to use the Unmanage Scheduling Utility on your primary application server.
The program allows you to use a variety of different methods to select the nodes that need to be unmanaged. We use Custom Properties to identify the node's Site ID in turn that Custom Property can then be used as a filter for the Unmanage Scheduling Utility.
Definitely a nice to have from the web console +1.
not to mention groups should be able to consist of nodes, component monitors, certain un-solicited events such as specific traps or event log events.....
This would be a huge benefit. I have multiple teams that have limited rights in SolarWinds. Grouping all of the stuff they care about into a group and giving them the ability to unmanage the entire group all at once makes life so much easier.