actually.... it all depends if this was one ticket or nested...

thezipper made a BIG boo-boo like this a few years back, was doing a DCA-DTW-CDG-DTW-DCA run and I forgot my passport at home... yup I was at DTW kicking myself soooo hard that night! But I went out to the counter and used a "trip in vain" excuse and they put me on the last flight back to DCA that night. Not sure if this will work for you, but give it a try.