My nephew ran out the spools that came with the weed whacker, so I had to get creative/lazy. I had a tube of various size zipties and the longest ones ended up being a perfect fit for the side feed hole.

A single ziptie did not reach the outer edge of the guard, but it got the job done. After breaking I was able to start chaining them, but I would not recommend that outside the cartridge enclosure. Direction matters a little bit just to ensure the rotation fires against the angle of departure, but it cuts either way.

A few more breaks and I learned the limits were similar to the standard feed (don't go for stiffer vegetation, rocks, or walls lol). Six ties or so and I was able to manage front and back yard just hitting the edges, high points, ivy, and saplings. Now I just need to find how to cut the zipties out, am certain I have a set of diagonal cutters around here somewhere.

Not sure if this hack is worth not getting the $1-2 spools, but my yard is even.

Hope this helps someone!