Here's my workaround:

1) From Google Drive export your document as a HTML web page

• File > Download as > Web Page (.html)

2) Use Sejda's HTML to PDF converter and the handy 'One long page' size option.

• Go to https://www.sejda.com/html-to-pdf
• Select the Convert HTML files tab and then upload your HTML file
• Click Convert HTML to PDF

By default the page size is 'One long page'. Can change it under More options.

If your Google doc contains images then when exporting to HTML you'll get a zip file. You can't upload a zip file to convert it to PDF, only the HTML file so it does't work great in that case.

Disclaimer: I'm a Sejda developer.