Actually the E-P1/E-P2 are different in operation in this regard than the E-PL1/E-PL2 as they have no dedicated button for manual focus assist. Instead it is a menu-driven option. I own an E-PL1 so I'm afraid I can't be of any more assistance than that. Perhaps someone with and E-P1 will be willing to post the steps required to activate MF assist with legacy lenses.Yes, but you will need to hit the little magnifying glass button to enable it. You'll also need to hit it again to disable it.
I've got an EPL2, just showed up yesterday, so I assume they work the same way.