Not after the tickets are bought. If you do this before the CO tickets are bought, they can add on the IB segments and charge you just once. You'll be protected in the event of misconnect, and you'll possibly even get a lower fare, as some of the taxes will be capped out.

Are you within 24 hours of original purchase? If so, you may want to refund the original tickets and start over. Be sure to make sure the original fare is still there before doing this, though.