Have you tried talking to your vet? Sometimes they can give you ear cream or drops which are easier to administer on cats with thick coats. The only other option I've used was to keep combing the back of the neck until the fur was nicely parted and I could see a little skin, but it won't work if you have a large drop to give.

I haven't done this because I don't have a cat yet. But to avoid stressing myself and stressing the cat, the only solution is to visit a vet and allow them do their work by themselves.