What I would personally do is to create a drum rack. Lets say you have a kick, a snare, and a hat. Nice and simple.
Then take that track in session view and create three midi clips.
In each clip create a midi not to trigger each drum note respectively.
So for the kick clip, create a kick; the snare, a snare; and a hat, a hat.
Depending on how fast you want your roll to be, change the duration of each midi note
AND the clip loop legnth to the much.
For instance if you want all sixteenth notes in your roll, make all the clips as such.
Then one you have all the notes and lengths how they need to be just create follow actions for each clip.
You will need to set each follow action to the length of the clip so it will change on time, and also its type to any.
This setting will allow it to create a psuedo roll when playing.
Now, the part where you capture it to see if you need to 'try again,'
Enable record so that this randomization will get paced in the arrangement view.
Click play and then start any of the clips that you have made.
This will start a chain of constantly changing notes in the duration you specified, yet in a random order.
If you get something you are happy with pause the playback and move to arrangement view.
Select the section that you like and press CTRL+J to Consolidate it.
Then you can click and drag it to the session view and paste it as a clip
It can then be named as a drum roll or added on to your randomization to have a bit of structure in the random playback.
This can all be expanded upon; For instance you can add more items to your drum rack. You could also create longer and shorter clips to give a different rhythmic variation. By doubling for instance the snare, and creating multiple variations this will allow for more interesting and rhythmic randomizations that can be somewhat controlled.
I hope this has been a little bit helpful. I know that it doesn't directly randomize a single MIDI part, but it can do what your're asking.
Cheers! 