Change InDesign buttons into hyperlinks to reduce interactive PDF size

Please help!

I have inherited a document that is set up with an interactive contents panel that when clicked on, aids navigation throughout the 81-page document. I have tried every way possible of exporting it as a reduced-size interactive PDF but there simply is no way of getting it below 70 MB. After exporting with and without the interactive element I realise that it’s the buttons (the contents and panel and the text links in it) that are causing the huge file size.

Because a similar document has previously been saved down to 20 MB by someone else (with the same working interactivity) I have asked how they achieved this. The answer was to ‘set up the navigation text as regular InDesign text (one not a button), then overlay the text with a free form, hyperlink.'

I have tried this but when I export the PDF, the now hyperlink (contents) text appears to be behind the contents panel (button) so it doesn’t show up or over the pop-up panel.

From what I’ve already read, I can’t see a way of making the text that was once buttons, hyperlinks without them being hidden due to the contents panel being a button.

I know this can be done as I have an example but am struggling to work it out! Please help - this is driving me nuts!