I haven't done anything with it. But I certainly do not intend to infringe on any trademark.
I'm at a loss to come up with a concept that does not likely infringe. "Fedex" is a unique enough term that it's not likely you were intending to do something unrelated to shipping. But, I don't want to jump to too many conclusions, so please provide some more background info if you don't mind.
fedexr.com = fede (short for federiko, my nickname in Spanish) + xr (for eXchange rates - I trade currency pairs).