Hi,
You are not able to do this now with any of the current software release.
In the upcoming TC4.2 release, for the c-series codecs, there will be a button on the top left corner of the touch screen that allows you to do that.
However, in EX90/Ex60, you will not see this button. For EX90/EX60, now you can already put the unit to standby by pressing the power button switch on the unit.