No it won't. LCDs aren't sensitive to that small amount of heat. (When an LCD is too hot or cold, it may not operate correctly, but when it returns to normal temperature, it'll be back to normal. Besides, iBooks don't vent much heat via the keyboard.)
Use Screen Spanning Doctor (I think that's the name) to enable lid-shut operation. Then you close the screen (which does sleep the iBook), but then you use an external keyboard to wake it.
tooki