Filip, stop beating around the bush, I'm waiting to see how a hazel warbow turns out! But here we are; (still) discussing the insanely complex device that is the stringer.
Maybe use that fishing braid as stringer material? Glue on temporary wooden nocks and use a double loop stringer. Problem solved.
Don't wanna use that braid? Use the belt you've mentioned, get some thick leather, make holes sufficiently away from the edge and "sew" the leather into pockets for the tips using the fishing braid. Male sure to use enough of it so that it doesn't just cut through the leather.
For heaven's sake just get on with the bow, one doesn't make a bow on the internet!