Kapinos was signed Tuesday following a tryout involving multiple punters. He averaged 43.8 yards on 66 punts last season for Green Bay, where he also spent part of the 2008 season. He was with the Colts for one game earlier this season, averaging 44.8 yards on four punts.
Sepulveda, injured against Baltimore on Sunday night, will have surgery Friday.
Tomlin also gave an injury update for the rest of his banged-up team.
"Heath Miller is experiencing the discomfort that goes along with concussions," Tomlin said Tuesday. "We'll see if it picks up as the week goes along. Of course, if we're going to err, we're going to err on the side of caution when it comes to players' health."
McClain was not penalized, but was fined $40,000 by the NFL on Monday for an illegal hit to the head of a defenseless receiver.
Tight end Matt Spaeth (concussion) has been cleared by doctors to return to practice Wednesday. While Spaeth is returning, right tackle Flozell Adams (high ankle sprain) is unlikely to play against Cincinnati (2-10).
"I'm sure there's going to be some level of discomfort," Tomlin said. "I don't think it's going to keep him out of football in any form or fashion."
Defensive end Aaron Smith (torn triceps tendon) has resumed lifting weights but won't be evaluated again for two weeks. He was hurt Oct. 24. The Steelers chose not to put him on the injured reserve list in case he healed in time for the playoffs.
Copyright 2010 by The Associated Press