Suppress a plate/spot ink for local printing?

I have a client in a common situation who's been looking for a solution for the past couple years. I thought the brain trust here could help out.

This publisher creates a 5-color textbook in ID CS3. The fifth color is a spot plate used for teachers annotations. It's applied to some text and some objects (like circles around correct answers). They can't isolate the 5th color on its own layer, since some of the annos need to be part of the text stream as inline objects. And some of the annos, like the circles, cross on top of other text and objects.

They send their printer a press-ready PDF of the TE (Teacher's Edition, with the 5th plate), and that printer has some sort of magical control in their equipment that lets them "suppress but overprint" the 5th color to create the SE (Student Edition, without the answers/spot plate).

I asked my client how an ink could be both "suppressed" and "overprinted" and she said she had no idea :-) -- that's what their commercial printer told her they're doing -- but that it's key, because it means you don't see knockouts from where the 5th color used to overlay other objects.

The client wants to know how to do this *themselves* in either InDesign or Acrobat, so they can create internal SE proofs as PDFs. To do so currently, they're working with 2 versions of the ID file, which is unwieldly for every document making up the textbook series. One version is the complete one that goes to the printer, in the other version they delete the spot color, replacing with None at the prompt ... the only way they can get an SE PDF (or print output for that matter) that looks both "suppressed and overprinted".

I can't see a way in Acrobat Pro to do this. Am I overlooking a control, or is there a script or a plug-in (they're willing to spend) for Acro that'll let them? I hear not even Pitstop Pro has this feature.

Thanks!

AM