Are you sure there is a sleeve or are you just guessing? If you route the cables with the housing through the frame there shouldn't be an additional sleeve.
See this quote:
"The plastic tube(s) that come in the frame are a tool, not a part of the bike. Feed the bare cable through the tube, pull the tube over the cable to remove it, then back-feed the housing over the cable to push through the frame. Full-length housings work here. To change cables, pull out the housing, push the tube over the cable, and pull out the cable to return to step one."