I take no credit for figuring it out. The instructions I followed are here:
http://www.kyphoto.com/classics/penees2repair.html
I will note, however, that I had to dig into it several times, first to deal with the aperture, then to address an intermittently sticky shutter. I strongly suggest you do both at the same time, and apply powered graphite to both; mine required it to work reliably.
The biggest issue is making sure you get the outer lens element dialed in correctly. I took several measurements as well as screwing the element all the way in before removing it, noting the sweep in degrees that it was from fully locked down. The author of the article above prefers the former method; I did both, but I think the latter is more useful. Regardless, that's the biggest issue. Everything else is quite simple really. Some tiny screwdrivers and snap ring pliers (easier than having a bunch of spanners) are all you'll need, aside from consumables.
While you're in there, locate the internal needle from the meter (look just below the viewfinder) and make sure it's moving as you point the selenium cell at different light sources. If not, your options are pretty limited, as you'll be stuck manually adjusting the aperture to deal with the default 1/40 shutter speed.
Further ruminations can be found here:
http://filmosaur.wordpress.com/2011/03/23/meet-the-camera-olympus-pen-ees-2/