I honestly have no clue why you would use black swordsman in your game. Is getting to that secret actually impossible without godmode or did you just bypass some triggers?
It is actually possible, here, I'll explain it to you with images (Spoilers ahead, beware.):
(X means fade away, arrows means where they go, squares are where they trigger, W is warp and S is a stopper (making the trap stop).
Descend into Hell Triggers:
(https://i.imgur.com/cW61lpu.png)
Black Swordsman Triggers:
(https://i.imgur.com/aQ8Hwaj.png)