You don't need 12 pitchers on Opening Day. You can get away with carrying 11 for a couple weeks, maybe three. It has been somewhat a standard practice to send the #5 starter to the minors to get a turn in the rotation for a couple weeks before he's brought up.
I think they did this with Wandy Rodriquez last year if I'm not mistaken. So when Scraps says an "extra" outfielder, I'm sure he means Bruntlett moreso than Lane. I count five outfielders right now: Lee, Burke, Scott, Palmiero and Lane. Bruntlett would, IMHO, constitute an extra outfielder because Loretta, Lamb and Quintero make up for the three infielders you carry.
Bruntlett is right though, if you want extra defense on the team, you keep him for the long haul. If you want a power right handed bat off the bench, you keep Lane.
I see them carrying Bruntlett for a couple weeks before they have to make a decision on him. He would need to pass through waivers if I remember correctly and he might not make it back to AAA if they tried to send him down at mid-April.
What may also happen is Garner changes his mind and believes that carrying the extra position player far outweighs the need for the extra reliever. I figure it all depends on the makeup of the pen. If you got guys who can pitch two to three innings each coming out of the pen (see: Borkowski and Sampson, maybe White), then you don't need to carry that many relievers. But then you have this: Lidge, Wheeler, Qualls, Miller as one innings guys, Borkowski, Sampson and White as two inning guys. That is seven, so if you carry five starters, you're at twelve guys. It may mean either White doesn't make the club for the long term or Bruntlett has to worry because they will indeed carry twelve guys. Sampson as a spot starter/spot reliever could change all that and cut down the need for a #5 and a long man all in one fail swoop.
I think this is what Garner wants to see if it works out that way.