You can use an external thermostat for managing a cooling call.  This is done by using CN35 terminal which is Remote ACC ON/OFF.  When close the cooling will be active.

Normally we set this up in automatic mode with hot water being priortity (both the hot water icon and cooling icon are displayed on controller).  I this mode the unit will turn on to first satisfy the domestic hot water.  As an example if water is set to 110 F the unit will turn on if the EcoULTRA tank fall below.  Now once the domestic hot water is satisfied, the unit will switch to cooling and cool until either:

1.  CN35 is open (no more thermostatic cooling call)
2.  Entering Water Temperature is satisfied (Water temp has been met by the heat pump)
3. Domestic hot water has fallen below the on threshold

If you don't want the domestic hot water involved you can switch to cooling only and use the CN35 to turn on off via your thermometer.