Our Harry's the same...hates treats (yep, we too have tried every flavour/shape/consistency known to man!) in fact he's not really food orientated at all....
Harry's favourite treat is his squeaky Kong tennis ball - he'd do ANYTHING for that...!!!
Others uses small pieces of cooked chicken breast, carrots, cheerios, small pieces of green beans, teensy little cheese cubes and (actually the one thing that Harry might eat!) tiny diced cooked chicken liver....makes me feel quite hungry...!!! Good luck!