My lost indoor new cat...help!?

okay..so in July we got a cat named Willie! he is very cut but he has been hiding for 5 months now and he always hides in the basement where its very cold.i sometimes find him there and i try to coax him to trust me,but he always hiss's.He scratches my best friend and he bit me and scratched me to!People are telling me to leave him alone for a while but it has been 5 MONTHS and I'm tired of people telling me that like the pet stores!If i try to get him out and hold him he starts to shiver and holds on to me so tight! If i let go he will run away!But know we know where hes hiding, in the ceiling!so if we get him and hold Willie he will just cling onto people or try to run away,he usually eats at night since hes kinda nocturnal.We cant give him back to his owners because they are flying to the middle east to live.plus i really love Willie because my old cat was his mother but i had to give Pinky away(my old cat!).Anything will help but please don't say leave him alone for a wile because its been 5 months now!and please don't say to get him to trust me because it wont work and i try'd!!thanks!