Sidenotes instead of footnotes

There's definitely a way but it will involve some work on your part. You'll need to make the neccessary changes to your template – this isn't a built-in feature of Blot. I'd consider looking into the bigfoot library, which is designed for working with footnotes:

Bigfoot.js

Note that Blot does offer some built-in layout options, which you can use to create sidenotes here:

Layout guide