In reply to Sarah: If you're setting boulder problems for yourself indoors it's probable that you're setting them to favour your dominant side. When I built my attic board I made it symetrical; ie: for every hold there is an identical one in the same place on the other side, and for every problem on it there is a mirror image version. This suits me as I only have to set half as many problems for a session. Also it's interesting that I try to climb the same problem differently, ie: using different footholds, depending on whether it's the left or right version.
To get back to your problem, if you don't have access to this kind of facility you could try the following:
Get a left handed friend to set problems for you.
finish every session with some offset pull ups and one arm deadhangs (use a bungee if needed).