I'm not sure what you are asking. At first I thought you answered your own question of "How can I show plain JMX attribute in RHQ" by saying "I found we can show only metrics of given MBean attributes".
But I think you are asking how you can the actual LIVE values of those attributes (as opposed to the past values that are being collected over time).
In the new RHQ 4 GUI, go to Measurement>Table subtab - there should be a "Get Live Values" for the selected metrics.
I think there is also a little "metric" icon in the graph views somewhere that, when you click it, you get a live graph that builds the graph in realtime. But I can't remember exactly where that is. Maybe someone who has a server running can post a screenshot of that?