Yes, you can. I called about it awhile ago because one of my friends had a bunch of comp WDW tickets. I was told you can't use comp tickets at Disneyland , but you can use any of the other kind. On the other hand, you can't use Disneyland tickets at Walt Disney World.
When you get to Disneyland, you will tell them you have a WDW PH ticket. They will subtract ONE day from your park hopper and give it back to you with a DL one day ticket. If you want to go the next day, repeat. And so on and on and on one day at a time.
Technically, you are not saving money since a 1 day ticket to WDW is more than a 1 day ticket to DL (which is why the reverse is not allowed), but if you are never going to use your WDW PH otherwise, then you are at least losing less money using it this way than to not use it at all.
Oh yea, are they the non expiring kind? I think the rule is if it's a park hopper and would be valid in Florida, then it would be valid in California. AP's, comp, and expired tickets are no good.