Is there a described algorithm converting _from_ Continuation Passing Style?
I did some additional research to answer this question but find nothing better suited.

To do reverse of CPS to direct programming you have to assign functions to variables, this makes direct structural code.

Automated and well described technique comes from compilers - SSA (Single Static Assignment).
This has additional bonus like compacting code and constant propagating to some extend.

This is not per se technique to reverse CPS, but structure of assignments creates direct code, so it is usable in your situation.