Thanks for that 2nd tip, Paul. I think it'll solve the problem. Basically, I'm publishing a thesis in both print and digital editions. Since it's about being a record producer, I want people to be able to listen to sound files while they're reading it. That's easy in the digital version.... not so easy for the print version.
I've decided to use QR codes and let people scan them with a handheld (smartphone, etc) in order to access sound files. I'll have the audio files stored on a website, and will also embed them in the PDF digital version. It's a bit inelegant, but it'll do.
Was able to create an invisible icon (1 pixel) to use when I do an "insert object" with an audio clip. I use the transparent icon. In the "Caption" box I simply typed a single space to leave it blank, and so it wouldn't revert back to the original name. I found the text gets in the way of the QR image.

But here's what I had to do in order to use a square QR image. After I created the "invisible" object on the page, I selected it:
1. right clicked it and "format object"
2. "colors and lines" --> "fill effects" --> "picture" (choose the QR graphic)
3. (still in "Format Object" window): "Size" --> H/W = both "Absolute"
4. first, UNLOCK the aspect ratio!!
5. I set both the height and width to 0.64" (a square)
6. Clicked "OK"
To resize the image, hold SHIFT while dragging a corner. It needs to stay square.

Seems to be working. The minimum size seems to be about 3/4" in order to get it to scan, but that's from the computer screen. Will print copies at various sizes to see how small I can get away with, but it should work fine.

Thanks again for your help. best, -john