What to do if I was unloading a truck for a customer at work and he backed up too far and pinned my hips together between his tailgate and the pallet of concrete?

You can make a personal injury claim with the customer involved and their automobile insurance carrier.  Since you have a valid worker's compensation claim, depending upon your state, you want to be careful about keeping the two claims valid.  It would be in your best interest to contact a personal injury attorney or a workers compensation attorney, if you do not already have one, and get a consultation about your rights.  

You actually have 2 cases. The first is your claim for workers comp. medical and income benefits. For the second, you should hire a lawyer. The second is a negligence claim against the other driver and her auto insurer. After proving negligence or carelessness against the other driver, you can ( through  a lawsuit ) recover a lump sum of money compensating you for your injuries, your pain and suffering, your disability, and any out-of pocket income or wage losses. You need a lawyer to coordinate this with your workers comensation claim. you amy have to reimburse the workers compensation insurer for the medical benefits paid to your doctors and the weekly disabilty payments to you.