Concrete Pier height increase

I have a porch that has 4 concrete piers below grade (about 12") and would like to increase the height of the concrete piers to bring the wood beams/posts above grade. Is it possible to increase the height of the pier by cutting a sonotube and placing it over the existing pier and pour concrete into the 12" section. I'm thinking that it may also be a good idea to drill the original concrete pier and place a stick to rebar into to connect the original with the new section. Any ideas? Is this a bad idea or is there a better solution?