I would wear a standard business suit. Trying to impress through sartorial elegance will, in a situation like this, backfire. Badly. If you truly do want to help your co-worker, then fudging the dress code will not assist you in any way. More, the kilt will distract, and will be seen as an attempt to deflect from your co-worker. Do everyone a favor, and dress in current fashion. Better yet, dress in the same mode as the boss generally does. Your appearance needs to be left out of the equation.