I have not had to deal with the 870, but the 753 document, I created my own custom tables and programs to generate. I never automated the process as we only had to do this for one customer for about 6 months.
As for the 754, we just printed off the Descriptive EDI format for the user. Like I said - not automated.
We have the same situation here... one customer, the NAVY! Sounds like you did exactly what we are attempting to do with the 753/754.
Under a huge time crunch to try and resolve because their request was not directed to us properly. Any chance you would be willing to share your setup or at least elaborate on the process?