heat the end with a flame and make a blob of plastic at the end. you can push a patch or spear it on the line and pull it through. it helps to look for the thickest line you can find. if necessary, double the line. if you double it you can spear a patch and pull it.
don't use a super tight patch. you aint cleaning out copper or carbon just some dirt or snow or light powder remains. just enough to save a blued barrel or clean out a muzzle if you tripped.
for real large bores like 12 ga i have drilled a hole in an old pistol case to pull the patch after i installed it on the weed eater line.