As I never have used QBW, but DCEW I do not know exactly. But it will something simple and easy like from command line...........
dbus-send --type=method_call --dest=com.nokia.HildonDesktop.AppMgr /com/nokia/HildonDesktop/AppMgr com.nokia.HildonDesktop.AppMgr.LaunchApplication string:"SIM1"
dbus-send --type=method_call --dest=com.nokia.HildonDesktop.AppMgr /com/nokia/HildonDesktop/AppMgr com.nokia.HildonDesktop.AppMgr.LaunchApplication string:"SIM2"