So, multiple gallows can be placed in the same place(you can probably see where this is going)
Step 1 place ALOT of gallows in one place(until you start lagging BAD)
Step 2 start throwing grenades
Step 3 wait till you get 100mil point(took me around 5 min)
WARNING!!!
you gotta have an above average pc (minimum 16gb ram) because while throwing grenades the game uses alot of ram(7gb for me)