This is a possibilty but James the Just (Jesus’ bro) who was the first Bishop of Jerusalem lived another 28 years until he was murdered in 62AD. Maybe Jesus wanted to free him up from that responsibility to build the church.
Sorry, but Christians believe that Jesus fulfilled the Law of Moses perfectly. If James had been Mary's son, Jesus would have been sinning seriously by taking from him his obligation to fulfill the mitzvah "Honor thy father and thy mother".
Scripture identifies James' father as "Alphaeus". He was most likely Jesus' cousin.