Pena will be available at Triple-A Round Rock either Tuesday or Wednesday.
The 36-year-old was released from a minor league deal by the Los Angeles Angels in spring training. Pena had a .207 average with Houston and Kansas City last year.
A first-round pick by Texas in 1998, Pena is a .233 hitter in 14 seasons with eight clubs. He has 285 homers, including six seasons with 25 or more.