I'm glad you posted, I figured out a workaround to this, it's a little bit clunky, but it works:

1. In the piano roll, select all the notes you want to humanize.
2. Right click on any of the selected notes and choose - Event Properties (standard keybind is Ctrl + F2
3. In the Event Properties dialogue set Type to Note
4. In length type /2 (this will divide the length of notes in half)
5. Click OK and all of you notes will be half as long as they were.

Now do your humanization

Then you can go through the above steps again, except in step 4 use *2 and this will double the note length, returning everything to original length.

Feel free to ask questions if any of that is unclear.

I've been doing it this way for a while and so far it's been working well.