Just curious, but does the user need to be able to edit the embedded PowerPoint slides, or are they just getting inserted as some kind of reference (e.g., sounds like maybe appendix materials or figures)?

If they don't need to be edited, another option is to save the PPT slides as images and insert those. Either option is likely going to increase the file size and slow the doc down, so I'd only do that toward the end of the process. You can compress the images at the end, but not sure how much it will help.