I'm with +Seb K
, probably would not recommend it. In some cases (hardtail frames with rigid forks) it's ok to increase the wheel size, but on a full-sus bike, even if there is room in the frame, you could end up in some not so good situations. Not only reducing tire clearance for debris, a small whack to knock your wheel out of true can cause the tire to hit the frame. I also know that on certain travel 26" Lefty forks, a 29er wheel can actually hit the bottom of the crown (VERY BAD) in full compression. More than likely the 27.5 would have enough room, but you never know.