Aw, how sweet! The answer is yes, he can be socialized! It's MUCH easier to do it inside only though. Is that an option for you?
There are a couple of ways to go about it.

Both will require a crate, so that's the first step. From there you have two choices.
The first step is to start putting his food in the crate so he's comfortable going in there to eat.
The next step depends upon what you want to do. You can either call around to local vets, and find one willing to give you a "flexible" appointment. I would tell them it's a skittish stray you want to adopt. If you can do this, when he's eating in the crate, be quick - but close the door. Then take him to the vet. In the meantime, get a room at home ready for him. When you come home, release him into the room. Kitties, when moved to a new territory, do MUCH better when in smaller space, and he'll socialize more quickly if confined to one room.

The alternative is to use the crate method - but rather than take him to the vet, you just release him into the room. The only problem with not getting him to the vet first is that he likely has fleas, and that can be a problem to fix once he's been inside before getting treated. (It's also best to assume he's got internal parasites, and the vet can treat him for those too). And getting him back into the crate to get him to an appt at a specific time can be a bit traumatic for both of you - but most of us have gone through it - you both survive!

FYI, we find that most feral kitties are actually so scared at the vet, they just hunker down and allow the exam.
To set up his room, the best thing to do is make sure it is kitten-proof:
http://www.thecatsite.com/Care/18/Br...a-New-Cat.html
I also highly suggest two litter pans, at least at first. Kitties from outside aren't used to peeing and pooping in the same place. But a non-clumping clay litter (at first) until he's used to using the pan - then you can slowly replace that with whatever litter you ultimately want to use (cats don't like rapid change, so best to change things slowly). In fact, if he's used to going in the garden, you may want to get potting soil, and put a thin layer over the tops of the clay litter - this will help him understand what he's supposed to do with the pans.

Often they'll lie on them at first - but eventually they HAVE to pee and/or poop. If he does either outside of the pan, if poop, scoop it up and put it in the pan - that's usually all it takes for them to "get" it. Same with pee - soak up what you can with paper towels and put it in the pan. Having the scent there helps him understand what the pans are for.

Otherwise, just spend as much time in the room as you can, and do things like scooping the pan, putting food down, cleaning his water dish - do each of those things on as regular a schedule as possible. At first he'll be scared and confused - but the schedule of doing things helps him understand faster that you're taking care of him. Especially the food - food is your friend with socializing. Same with having a scheduled play time.
But spend as much time as you can with him/her in there - but spend a lot of the time NOT trying to interact with him. You'll be big and he'll be scared - so get down on the floor, and read out loud. Sing. Sew. Fold laundry. Talk to him in a soft, quiet voice, and while sometimes try to engage him interactive play (like with the shoestring, though there are toys designed for this), spend a lot of your time just talking or whatever and not trying to interact. Do whatever you can in there, and just let him get used to you being NOT threatening. He needs to get used to the new sites, the new sounds, the new smells!
Here's an article you may find helpful:
http://www.straypetadvocacy.org/soci...feral_cat.html
If you want to work with kitty outside, it will take longer - likely a lot longer. But the basic principles are the same. Spend as much time as you can being non-threatening, not trying to interact, but do everything as much as possible on a schedule - the most important part being that kitty associate you as the person providing his food. And sit while he eats, talking to him, not looking at him.

It's our instinct to want to love all over them - but they take their own time getting there. But once they do - there's no bond like it.
