There is no way to do this using your TiVo. However, you could download all of the shows to your PC and then use video editing software to make one large file with all of the content you need, then transfer the larger combined file back to your TiVo. However, this is a lot of work, especially if you need to do this regularly.
Sony S2, SVR-3000, lifetime (11/02)-160GB drive upgraded 11/04 (limited to 137GB)
TiVo S2, 540 unit, lifetime (7/05)-250GB drive upgraded 5/06
TiVoHD, lifetime (10/09)-1TB drive upgraded 5/10