The consensus on this independent Atkins Forum is that no extra intake is needed.
http://www.atkinsdietbulletinboard.c...406&highlight=
You will, of course, be able to stay in ketosis at a higher input of carbs when doing this cycling or any other excercise.
Since I started cycling I have seen some very deep purples on the ketosticks and that is with eating more and drinkings large ammounts of water.