Or how about my cheap blade and some patience? I just snuck downstairs to test this idea out:
I scored both sides of the valley and popped it out quickly in small bits to the depth of one ply. It's actually pretty easy to remove if you stick to ply-depths =)
This took maybe 2 min. I'm going for it after I do a test going with the wood grain as well. Used the piece of drywall sanding screen to quickly sand inside the valley. I know I could do this even cleaner but once I paint this will easily look good enough.