I recently attended a weekday morning minyan where the Torah reader was reading simultaneously from a sefer Torah and a printed Chumash. It appeared that the person was mostly reading from Chumash and moving the yad to follow along in the sefer Torah. The usual liturgy before and after the reading was said as were the blessings before and after the aliyot. Is this a valid practice?
The Rama (OC 143:2) writes:
I can't comment about the specifics of your case, but in general one may not recite the blessings and perform the standard Torah service using a printed Chumash; however, when no one has prepared the reading, it's possible to have a prompter use a printed Chumash so long as it is read for real out of the kosher scroll.
 Reading from a written Chumash is a whole 'nother story, but you don't see those around too often anymore.