I agree with moosmom. I believe you can socialize a feral..it just takes lots of time and patience and the older the kitty is, the more of each that's required. A separate area is a must. I took in Scout at 11 weeks. He was feral. Would run from you, hide, hiss horribly if you tried to pick him up.

I kept Scout in the bathroom for the first week. Little eye contact was made. He was forced to spend time with me. Lots of chicken baby food was consumed. I even read to him whatever book I was reading in a soft voice so he could get used to the sound of me. You mentioned finally being able to corner him and gave a treat. You might want to consider confining him to even a smaller place such as a bathroom to work with him until he gets a little more comfortable around you. Scout didn't have anywhere to hide in the bathroom and had to be near me. Within the next couple weeks...now confined to the bathroom and kitchen, I held him a lot. He didn't like being held and would struggle if I was sitting down..but was ok if i held him as I walked around.

It only took a few weeks for him to be lovey towards me, but he was younger than your kitty. All I can say is lots of time and pateince. The more time you spend with kitty...even if he's screaming is best. Eventually he will start to associate you with good things like being fed and treats. Good Luck!