For a 5/8" hose with a coupling at only one end, cut off 1" of 3/4" ID copper pipe, make a lengthwise cut, deburr the inside, expand the cut opening to 1/4", slide it to the last kink in the hose and work your way up to the first kink with more fittings, then squeeze each closed with pliers.
The hacksaw works better on this thin-walled pipe if you have it cutting in the pulling direction.
Sometimes a scrap garden hose is the right answer. but if you have to do this much work to make it work, get a better hose. maybe use a scrap washing machine hose. Or visit the back aisle at HD and see what kind of tubing they offer.