If you haven't seen the last video about drones, please go back and start there!
Here's the link to the drone tracks: http://selz.co/VJFhoPYhW
After you've started feeling good about playing in all 12 major keys, I would move along to this exercise playing the chromatic scale against the drone.
The same slow and patient approach is key here. Take time to be especially mindful on the more dissonant intervals, they can be the most challenging ones to tackle.
I encourage my students to do at least two octaves if not their whole range. Make sure you tune each interval relative to the bass note!
Let me know about any questions/comments/concerns...