There are commercially available products that are inexpensive and affective.
Here is an example from West Marine in the USA.
http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&productId=24814&catalogId=10001&classNum=784&subdeptNum=625&storeNum=6
I have also seen a simple rubber "transom pad" that simply sits between the clamps and the transom.
One could also easily make a nice looking pad out of aluminum plate. It is easy to cut with power tools and easy to mount.
Good luck.