I would trap him, s/n, shots and release him after a day. IF you want him to be an indoor cat and you don't have a spare room to socialize him I would let him come and go as he wants. He will start spending longer and longer time once he starts to feel comfortable in your house. It all takes baby steps and short interaction with him in the house. It took us 4 yrs to make our faux feral a house cat. He did it at his own pace with gentle nudges pushing his boundaries of petting, lifting, holding, etc.