Originally Posted by Commander Keen
-Punch a hole in the top/outer edge of the filter with a screwdriver and hammer.
-Wait about an hour.
-Proceed normally with oil change.
I'm not patient enough to wait an hour, especially since I've been able to avoid a mess without this extra wait time. I've never had significant (if any) amounts of oil drain from my old filter during an oil change on this Impreza, so I guess the filter's internal valve is doing its job.
If I'm ever not able to buy the black Subaru/Roki "160" filters anymore, I hope I can find another filter brand/model that behaves this way.
EDIT: If someone tries the highly-regarded Fram XG7317 synthetic filter, I'd be curious to know how well it holds the oil during removal.