By doing the sufficient antihistamines I'd guess?
Diphenhydramine(nytol, other names) or promethazine(mainly Phenergan) seem to work for me for itch killing (and also strengthening the nod) both cheap and legal and otc.
Atarax was good too, stronger nod enhancement imo, although thats a brand name not the chemical name.
Keep the dose low when I was dependent on opiates I'd never get much itches if I only took a low dose. It's when you shoot a big shot of heroin you get itchy.