Unfortunately energyXT2 does not have a "tempo track" like version 1.4.1 does. What follows is a workaround using a MIDI loopback device with the Controller Map.
For MIDI loopback:
Windows - use a virtual MIDI driver.
Mac OS X - use the IAC bus.
Linux - make connections with qjackctl.
For best results, use one of the available MIDI output VST plugins rather than the built-in MIDI Out component.
The tempo will be double the CC value. For example, to set the tempo to 120 bpm, create a CC event at value 60. Use the event list or a MIDI monitor plugin to see CC values. Note that the tempo is still limited to 10 through 250bpm, so that CC values 5 or below will be 10bpm, and 125 and above will be 250bpm.
Remember to avoid MIDI feedback!