Ideas..
I don't know the 'real' answer to your question... but some ideas:
1. Delete the entire back-up... partition the TC to only allocate a fraction to your TC to the back-up process and the other part for usable storage space -- and then restart the TC back-up process fresh. I honestly don't know if you can do this with the way the TC media is mechanized, but I did this with a non-TC external before I bought a TC.
2. Don't do that at all, and spend ~ $40-50 for a second external drive. One of the features of the TC was your have long-term 'snap shot' in time of your files you have and once had. New storage is cheap ...
Good luck ..