There are a couple of ways to do that...  you could render the loop down and play it in an outside media player and then play to that, realigning everthing when you are finished.  You could also just lay the loop out for a few bars or however long the loop is you are wanting to record and then just record it...  seems fairly straightforward.  For the second one,  Wherever you set the cursor in the playlist is where you will record from...so, if you set the cursor a little before the beat begins then you will be able to record from that spot.  I hope that answers the question..if not just hit me up here or in PM.