The following is a script to enable drag scroll for a trackball:
-- HANDLE SCROLLING WITH MOUSE BUTTON PRESSED
-- Use button right click
-- Use button 3 for kensington back button
-- Use button 6 for Elecom Deft Pro
local config = {
    scrollButtons = { 3, 6 },
    rightButtonScrollEnabled = true,
    scrollSpeedMultiplier = -4, --