As a crude idea for the hole itself, get the hole attached to the wall as a decal.
These are just ideas, open to everyone for comments. Ive never tried any of them...

Then while the player is 'touching' it, or 'penetrating' it, try one of the following...
1> move the player with the IGNORE_WORLD switch in its c_move.
2> move the player with the wall set to YOU, and the IGNORE_YOU in players c_move.
3> move the player with simple XYZ adjustments rather than c_move.
4> make that wall PASSABLE. If its a level-block, try setting 'level_ent' to passable,
or do the players c_move with IGNORE_WORLD.
5> make the wall and the player have the same "group" property so they ignore collisions
with each other (check the manual under c_move, 'IGNORE_PUSH' section).