The lever push up is a great suggestion. They work really well if you have access to a ball, any kind; medicine ball, basketball, soccer ball etc. You place the "off" hand on top of the ball and allow the ball to roll off to the side while keeping that arm straight, as you lower down. Placing most of your weight on the bent arm, press yourself back up while returning the ball. Sort of hard to describe, <a title="Lever Push Up" href="http://www.youtube.com/watch?v=QgS-SRHS7wI">HERE'S</a> a video.
The one problem with lever push ups is that they are much, much more stable than true one arm attempts, I've known people who can do 20 lever push ups, but don't have the necessary tension to perform even one arm negatives. They are good for volume, but you want to make sure to include other progressions too, negatives and ISO holds definitely helped me to work on the groove.