Mikel Leshoure or CJ Spiller in my flex?
Well Houston has held Reggie Bush, MJD, Willis McGahee, and Ray Rice to under 100 yards and haven't allowed a rushing TD so far (IIRC). And The Texans might take quick lead and force the BIlls to abandon the run for the most part. Even though Leshoure will lose some carries to Bell, I think he might be your best bet.
Flex help (Choose 1):
1 PPR, 1 point for 10 rushing or receiving, 6 point per TD Vick Ballard
vs. Miami, Cecil Shorts
vs. Detroit, Ryan Broyles
vs. Jacksonville, or Greg Olsen