For what it's worth, when I'm debinding magazines, I take an old punch card (essentially the same size and shape of a credit card) and gently push/scrape the glue off the edge while applying heat. This isn't a perfect solution, as there will typically be a faint residue that will smear instead of coming off, but I find it easier to edit out in Photoshop than a solid lump of glue. Of course, the question then becomes how much effort you're willing to expend editing versus cropping it out completely. Also, I use a flatbed scanner, so I have no clue how scans using that method would turn out in an ADF scanner.