A story I read a day or two ago said Tice was shuffling his interior line to compensate for Birk's absence. The article didn't specify names.
The story excerpted above says:
Tice chose backup Cory Withrow the starter at center, moved Chris Liwienski from right guard to left guard, inserted rookie Marcus Johnson as the starter at right guard and moved Adam Goldberg from starting left guard to the primary backup at both guard spots and center.
Once viewed as a makeshift unit until Birk's return, now it appears that will be the offensive line for the majority of the season.