Unfortunately the only way to sedate him would be to take him to your vet and get a sedative. Though if you go to your vet you may be able to explain the situation and he may give you something to give him.
If you can get him to trust you enough to put a leash on him you could take him in and get him examined and cleaned up enough to make him well.
He really needs some attention as stray dogs are so often lost to illness or other peoples bad behavior. I would recommend calling your local no kill shelters such as Little Victory's and ask if someone can come pick him up. They can get him the vet treatment he needs and help find him a forever home.
Is there someone who could assist you with getting him to a vet? A full stomach will help settle him down some. You may want to try a localize numbing agent to numb the areas that need clean. You can pick these up over the counter such as Neopsprin with pain reliever or another numbing agent.
You could also try luring him into a small crate or cage and then working on him though the bars to prevent him running off. If you are no fearful of him biting you you could try a leash to hold him still while you work on his ears.
Benadryl by mouth, can be used as a mild sedative and make make him feel a little at ease while you treat the ears. Typical dosages: for dogs under 30 pounds, give 10 mg ... dogs 30 to 50 pounds, give 25 mg ... dogs over 50 pounds, give 50 mg. Use only the plain Benadryl formula the pill form and never use the liquid as it is to strong a dosage. I typically do not suggest this as it is better for a vet or groomer to take care of these things but since this is not possible you can use the benadryl.
After removing the ticks you need to clean the spots with hydrogen peroxide and use some neosporin with pain reliever on it. This is a one time shot because you don't want to be giving him another treatment of the benadryl so make sure you get him completely.