I can see in your photos that is a Ryobi PLT3043 trimmer. I have been doing this for years but I used a wire. Your idea is not a bad idea. How I do it is I used a 1.2mm x 25cm long stainless steel wire with hook on the other end and a key ring on other end. Other tool I made out of a throttle cable I use to hook the line or fuel filter off the cap opening. Please see photos.
