Here is a method, but, it has to be created in Acrobat, not Indesign. Your boss can use either Acrobat or Reader to add logo.
Close Button Properties, and Save PDF.
Then your boss can open PDF. When this button is selected, you can browse and select external logo to be added to PDF. Here are some restrictions: image format needs to be PDF. But most image formats like jpeg can be easily converted to PDF by simply opening in Acrobat. The logo can be sized in Acrobat only, not Reader.
That's perfect. I can supply the .pdfs as I created all the logos and have the native .ai file.
Now that it does exactly what I want it to I'm having an issue. I link the .pdf but the button is blank. The logo doesn't show up. I click it again and I can see it is linked and it's not coming from a network but the page itself shows blank. What am I missing?
Sorry, I forgot one step. When you have the Button Properties open, select the Options (tab). Under Layout (pulldown) select "Icon Only"
Great! That's exactly what I need and it works perfectly.
Thank you for your time.