
I do feel sorry for you. I hate to see the forced method used, it can put a sensitive dog off for life. I will try and help you with some suggestions, but first of all don't try the dumbell with him at all for a couple of weeks.
What is the centre of the dumbell like? Is it hard? If so, try putting some cloth around it to make it softer in the mouth. Or what I did was put lots of masking tape around it to soften it.
It sounds like both you and him understand the clicker. The idea of the clicker being the dog works out what you want by himself, you click and treat immediately. So, kneel down on the floor, just hold the dumbell infront of him, if he looks at it, click, move on to if he moves his head towards it click, then the big step, if he touches it click. Don't rush these stages, they will take time as he has been put off of it. These are your foundation steps. At anytime later he refuses to take the dumbell, always go back to these.
When you have him confidently touching it and happy about it, hold it towards the floor and repeat. Eventually putting it on to the floor, keeping your hand on it at first, then taking it away. At no stage are you asking him to hold it, just be comfortable with it. After he is happy with this, withold the click until he puts his mouth around it, then click. I am sure you are getting the idea now, hopefully you can build this up until he picks it up. As soon as he does pick it up, click immediately, let him drop it and get the treat. You can then build up the time he holds it for before you click.
Don't let your trainer anywhere near him at this time, you will have to be firm, otherwise everything you have acheived will be undone.
Don't rush any of the steps, take your time, build his confidence.
Good Luck, let us know how you get on.