You can either do
THIS. Or you can Overload the map using a different techinique.
Step 1: Go in Forge mode and go to the equipement pallet.
Step 2: STAY STILL!!! Do not look around or move.
Step 3: Keep spawing equipement. Grenades, Bubble Shields, Etc...
Step 4: Keep spawning untill the mancannon is disabled. If you do not know if it is active or disabled, get another controller and sign in a guest.
And there you have it.