For the past 4 years, (and the majority of his carer), Blum has been terrible as a right-handed batter, so there is no reason to think he will magically get substantially better this year. I think if we start seeing Tejada at 3rd over the next week, we'll see the Astros' plans.
Manzella hit .219 last year at Round Rock with zero home runs and zero steals in 221 ABs. In fewer ABs, Chris Johnson was equally bad at AAA (but he did well at AA). I personally don't think either is ready for the Majors. Blum was bad, but he had a better season in Houston than either of those guys did at AAA. I'd look for outside options if possible.
