529 and Work Tuition Reimb without Double Dipping

My work offers an 80% tuition reimbursement for certain qualified education expenses, up to $40,000. My school is charging about 25k per year. I know that approximately the first $5,250 is tax free, but what if I choose to filter the rest through a 529 plan? Can I get another 10k to be tax free this way? And to take it a step further, can I apply 529 savings to student loans in future years, or only in years that I incurred the expenses?