T.R. Sullivan says that it looks like Robinson Tejeda is going to stick in the bullpen as a second long man (along with Jamey Wright), with the Rangers liking his arm and not wanting to risk him getting plucked off the waiver wire by another team.
Sullivan says that Franklyn German has the inside track on the final bullpen spot, although Wes Littleton is also in the mix. The Rangers will keep 8 relievers until April 12, when Luis Mendoza or Kason Gabbard will get called up to take over the 5th starter role, so Littleton could make the team initially only to be sent down after a couple of weeks.
What complicates this is the 40 man situation. German and Wright are both on minor league deals, meaning they'll have to be added to the 40 man roster before Opening Day. John Rheinecker will go to the 60 day d.l., which opens up one slot, and Nelson Cruz will either be traded or DFA'd, which opens up another.
However, it seems likely at this point that Adam Melhuse will have to be added, as well, as it appears likely that Jarrod Saltalamacchia will start the season in AAA. There's no obvious spot that can be cleared for Melhuse (and before you suggest Jason Botts, if Botts doesn't make the team, Kevin Mench will, and Mench would take Botts' spot on the 40 man).
Travis Metcalf or Thomas Diamond could go to the 60 day d.l., conceivably. But if someone doesn't go to the 60 day d.l., the Rangers are going to be in a roster squeeze, because there is no one out there who looks like an obvious choice to get whacked from the 40 man roster.
My guess is that, if the Rangers decide to go that direction, you'll see someone like Littleton or Kam Loe dealt to a team that needs relief help, like the Tigers (whose manager is predicting they will make a deal in the next few days) or the Phillies. The Rangers have a lot of bullpen options, and both Littleton and Loe could contribute in a middle relief role to a contending team.