L2capitalize.
Sure, you "can" run heroics as 17/0/41 +3 (etc,etc)... I "can" paint my house with linguine noodles too. Hmm... actually sounds fun...
Anyway, if you're very good and over-geared then you can pull off decent DPS as a Sub spec rogue in PvE heroics. I've seen it myself. But, seriously, respecs are cheap. Just run a couple of quick dailies and respect combat to run PvE content and stop being lazy.
ShS is generally not considered a dagger build. Ambush is fun and all, but at that level of the game it just doesn't stack up to your other options.
Good luck.