Check out the video on this page called 'Inserting a needle into destination row, before unraveling' http://www.knittinghelp.com/knitting...iques/misc.php
Amy is using a piece of ribbed knitting to demonstrate. Instead of reinserting a needle, you are wanting to insert a lifeline, but it is the same principal. And since with ribbing it is switching between knits and purls, you should be able to get some tips.
Good luck! :XX: