There is an API entry for UseCompression (look in the APIGuide) that allows true or false, although the document properties allow None, High, Normal (so true may be high or normal). From the APIGuide:
set up = ActiveDocument.GetApplication.GetUserPreferencesup.UseCompression = trueActiveDocument.GetApplication.SetUserPreferences up
Haven't tested though. If that works, then you can set, say, a document with a button and execute this as a macro in action.