I do it by myself, but that doesn't mean that it sometimes feels like I need a third hand...
I use an air pump sold for inflating air mattresses and the like. I usually have some idea of the general location of the leak. So, I "paint" the suspect area with the soap solution, shove the air hose down that leg and constrict it with the same hand that is holding the hose in place through the material. Once I find the leak, I circle it with a bright crayon, repair it and then when the wader is dry, I take an old kitchen sponge and scrub the colored crayon off. I used to use sharpies to mark leaks, but then I was walking around on the creek with waders covered in little black bulls eyes. The crayon is better. I like mango orange and lime green best...