Within the current implementation, the Fist gesture triggers instantly upon touching the trigger. Implementing a customizable GestureWeight option to the Marker creation menu would allow users to require a slight or full pull of the trigger in order to start drawing. I currently have the Marker modified on my avatar to require a 0.5 gesture weight in order to trigger either drawing or erasing, which I feel would be a good default value.
This would require a slight edit of the existing animators- specifically to include an extra entry condition, as well as an extra exit transition for both the Drawing and Erasing animations.