One option would be to have the characters have been the original team that tried to save the great Modron March. In one of the trips through the outlands they failed to stop a large contingent being lost and this triggered the glitch.
I think it would be a cool idea but as none of my players know that adventure it would require a lot of seeding of ideas into the game. It might be a bit much.
Just out of interest, what elements from Torment would you want to add into the game?
The expansion of the Mausoleum.
The Smoldering Corpse Bar - with a decanter of endless water somewhere.
The Civic Festhall
The Brothel of Slating Intellectual Lusts
The Art Gallery
Expansion of Curst.
The more I think about it the more I feel that the gate Town visits are pretty banal. Too simplistic, too mundane, mini adventures is an understatement.
I think I would prefer to run fewer gate towns but take things into some other weird and wonderful locations and spend a bit more attention there.