Wallace, 25, will play first and third base with the team. He is also considered an option at shortstop should current starter Marwin Gonzalez get injured. Manager Brad Mills said infielder Matt Downs is also an option.
"I think if something happens with [Gonzalez], I don't have any problem at all putting those guys out there for a few innings," Mills said. "Then we'll go from there."
In 36 at-bats with the Astros earlier this season, Wallace batted .333/.426/.583 with two homers and four RBIs. With Oklahoma City, Wallace was batting .300/.379/.506. Over his last 10 games, Wallace was 11-for-32 with two homers and eight RBIs.
Wallace played nine games at shortstop with Oklahoma City. He has no other shortstop experience in the Minor Leagues.
Bixler, 29, batted .193 in 88 at-bats for the Astros.