If you jump to the boss without activating the boss, the protective bubble won't spawn for a brief moment, and your passive damage can kill it.

Then you can just jump through the wall to reach the final boss (with Havoc Metamorphosis / Vengeance Infernal Strike / Heroic Leap [Cogwheel]). However it's easy to fall down after. The most consistent way is to move forward a tiny bit after the wallclip and triple jump out.