You can't. Many languages are having to develop non-sexist terminology and that leads to all sorts of problems.
Increasingly duine is being used for 'person', as there is, conveniently, another word for 'man'. I suspect that soon duine will only mean 'person'. Dwelly (1911) says
duine gen sing duine, pl. daoine, sm Man. 2 Person, body, individual. 3 The oldest man of a village. Duine gun mhath gun chron, is motha a chron na a mhath, a man that's neither good nor ill is more ill than good — duine gun mhath gun chron, is also applied to a shiftless, thriftless sort of man who is otherwise quite decent; an duine, the good-man of the house; an duine agam-sa, my husband — duine is often applied to either men or women, as, a bheil duine a-staigh? is anyone in? is fheàrr duine na daoine, a proper person is better than many men; ro-dhuine, an excellent man, man of rank; fiadh-dhuine, wild man, satyr; duine gaoil, a male relative; duine math, good man; duine nan clag, the bellman. Fear de mo dhaoine, one of my men, is a good example of the difference between fear and duine.
Mark (2003) says
duine , pl daoine nm anyone, man, man (husband), mankind, nobody / no one (with neg verbs), person, fellow, one □ shaoileadh duine bho na chaidh a ràdh gu ruige seo gu…one would think from what has been said so far that… □ a dhuine! dear man! □ duine uasal gentleman □ a dhuine uasail sir, dear sir (in polite address or in letters) □ a dhuine uasail, am faod mi a ràdh …? sir, may I say …? □ an duine aice her man / husband □ nuair a bhios mi na mo dhuine (mòr) when I am a man □ an duine (also an urra ) each pron □ phàigh sinn còig notaichean an duine we paid £5 each □ duine dìolain bastard (of an illegitimate child only) □ duine dubh negro □ gheibh gach duine cloinne ceithir leasain every child (lit. person of a child) will receive four lessons □ daoine mòra big people (it should be noted that though daoine has a slender ending the adj is not lenited – an exception to the general rule)