While that would be nice, you can't do it in MMM. In the end, it's not really necessary.
As I 'm sure you know, the computer keyboard can play a little over 2 1/2 octaves with a slight overlap in the Vita MIDI editor. There is no "shift octave" key to change the octave you're playing in. So, you have two options...
If you want to transpose an entire MIDI object, you can do that from the MIDI object menu....(MIDI Object Menu) > Tempo & Pitch > MIDI transposition... (Alt+Shift+D) You can choose the number of half-tones (semitones) you wish to transpose.
If you need to transpose only a few notes, it is very easy to do in the MIDI editor. Hold the CTRL key and highlight all of the notes you wish to transpose by the same amount. Then, simply click and drag them higher or lower on the Vita arranger. You can also do this to the entire MIDI object in Vita by selecting "Select All" (CTRL+A), then click and drag the entire group of MIDI notes up or down.