No, you're bzggered.

If you have a reservation that you do not use, all subsequent reservations are autocancelled.

But ask your T.A. this question, assuming that you have a paper ticket. Could you cancel the first sector and pull the first coupon out yourself? Do not ask the T.A. to cancel it - he/she runs a risk of being charged $$$ if LH figures it out. You would have to phone LH and do it yourself, making sure that the downline flights aren't touched. This is a desperate measure and I don't have all that much faith in it, but ask anyways. They can't charge you more money after the fact without your permission.