I just tried a little experiment… trying to get a breve with Step Input, and not really holding out too much hope…. but it worked! 
There’s a one-off operation to perform…
- Create a MIDI Part, say, 2 bars long, in either 4/4 or 2/2
- Fill it with breves
- Close the Editor, then, from the Project window, select the MIDI Part, then Edit menu>Advanced Quantize>“Create Groove Quantize Preset”.
This new Quantize Preset is now available in the Quantize Menu, and works exactly as you would like when doing Step Input.
(No-one is more surprised than myself!
)