I agree that the best idea is start with the source...in the meantime, maybe this will be useful...
In Poway we have Edco as our waste company, they only take 1 and 2 plastics, so I have saved my 5's and 6's and taken them down to the San Diego recycling center off of 52/Convoy. They will take them if they are separated by number. It appears that they will even pay you for them - but there was a bit of a language difficulty when I was there and I didn't really care if I got any money or not, so I just gave them what I had.
What I don't know for sure is if the stuff actually gets recycled - or do they just say they recycle it? Anyone know for sure?
I have heard that you can take your plastic stuff to Cactus Recycling too. In fact, a few months ago when La Mesa had their sustainability fair, Catus was there and taking all numbered plastics.
If you hear of a better way, let me know. I have a couple trashcans full of 5's and 6's.