http://s177.photobucket.com/albums/w...t=IMG020-1.jpg
I hope this poor quality image helps. This is a frugally rebuild image of the final arm lock (this round made with the left arm, because my silly camera couldn't make the photo better than in that position). If from that situation you step forward and you tenkan, your hand will exert pressure on uke's locked arm and bring him down.
This may work only: right arm traps right arm, or left arm traps left arm.