Ya, I don't see how a solo-play of a non-solo game wouldn't count, when solo games count fine on their own. You're basically playing a variant.
I think I'll add Lord of the Rings Card Game to my list. That's another hard one that I only played 1.5-2 times, mostly to try and figure out the rules. I started watching rules explanations last night to relearn it, and I bet it'll be fun to try and complete the quests from the core box.