My cat developped bumps on his ears recently and I had great success in completely eliminating them with "Bach Rescue Cream" an homeopathic remedy that I have used on myself and my whole family for skin abrasions, cuts and even burns. It is a wonderful cream, along with the other Bach products available in health stores ($14.99 CDN for 30 grams).

Put a small amount on the tip of your finger and gently (these bumps seem to be painful) rub on the exterior of the ear until completely absorbed. The area will still appear "wet" when you're finished but dries out shortly. Do this twice a day (once in the morning, once at night) for about 1 week and all the bumps should be gone by then. Should they ever come back, repeat the procedure. It also works wonderfully on cat acne and either procedure takes very little cream, is safe to use and does not contain chemicals. I have used it on my dog as well on skin irritation where he scratched himself too vigorously. I have yet to see it NOT WORK in restoring and soothing any skin surface, be it human or animal.