Bontrager offers a carbon seat post ($100) that has an aluminum core which would allow you to add a seatpost rack and carry up to 25# on it, but I'm not sure I would put that much weight on a seat post rack.

Or you could just put on an aluminum seat post - cheaper for sure.

You didn't keep the Trek? Too bad. You will probably find you have as much use for a road bike as you do a hybrid. Then a commuter. Then a mtb... it never ends.