You know, I did an imperial stout last week with that very same yeast. Granted, mine was a mason jar full of fresh trub pulled from a conical at a local brewpub, but same yeast and all. I didn't do a starter, because it was freshly pulled from an active conical. And lagtime was LONG. Started VERY slow. Took awhile just to see a real krausen. Oddball. But I tried some last night. very good, but strong as a muf*ck. Went from like 1.095 to 1.030.
Anyway, if I were you, in the future, if you're doing one of those "last-minute" brews, try not to make it a high-grav one. They're the most brutal when it comes to needing a starter.