So, the reason a provider will tell you to add a script just below the closing body tag is because that script references some element in the DOM that it tells you to provide.
Which basically means that the script should be run after page load. So, you can use my LOADERR plugin for that (but it doesn’t let you provide plain text for your script, so just upload the script in question to Bubble’s CDN and use the URL from there). How do you upload some random script to Cloudfront? Just do this: Does Bubble use the unpkg CDN? - #8 by keith and then you can use that URL in LOADERR.
Plugin page for LOADERR: LOADERR: Load JavaScript Libraries Plugin | Bubble