Sneak Attack doing nonlethal damage with a lethal weapon? (+AWESOME INTIMIDATE BUILD)

[rahimka]

Can anyone clarify the RAW on Sneak Attack while doing non-lethal damage? Specifically, when doing nonlethal damage with a typically lethal weapon, is it even possible to be adding one's sneak attack damage? I figure this would HAVE to be lethal if so, but I'm not really sure if its even possible.

The specific situation: An Ifrit Unchained Rogue with the Blade of Mercy trait uses his daggers (as slashing melee weapons) to do nonlethal damage. I understand that he can't do nonlethal Sneak Attack because BoM doesn't make the daggers a "nonlethal weapon", it just lets him ignore the usual -4 penalty on his attack roles. But can he be doing LETHAL sneak attack on top of that nonlethal weapon damage?
EDIT: Clarfiying, this is PF not 3.5

PS. btw, I highly recommend this build (doable at lvl3 w/TWF) for a really fun melee striker/debuffer:
Blade of Mercy (religion trait): nonlethal damage with any slashing melee weapon, +1 damage when you do this
Enforcer (feat): free Intimidate checks when he does nonlethal damage (for rounds=damage instead of the usual duration)
Fiery Glare (Ifrit trait): can always take 10 on Intimidate checks (useful to auto-succeed and avoid excessive dice rolling)
Thug archetype: +1 round to any Shaken effect, if you inflict shaken for 4+ rounds (see Enforcer) you can make it Fear for 1 round instead, get the option to drop 1d6 sneak attack to inflict Sickened for rounds=lvl/2
Unchained Rogue: +dex to damage on daggers (see Enforcer), and at lvl4 add Debilitating Injury when sneak attack is dealt

He's also got the Scout archetype so its easier to get sneak attack opportunities. I picked up Dazzling Display at lvl 5 (so he can send the room running in Fear for 1 round, or at least leave them shaken for several) and will add Shatter Defenses when he gets to high enough level (need BAB +6)

LONG STORY SHORT: he's dishing out solid damage and/or serious STACKING debuffs (shaken, sickened, & debilitating strike) and/or action denial pretty much every round.

Being able to add his sneak attack (for lethal damage) even when he does nonlethal with his daggers would just help him apply all those stacking debuffs a little faster

[nedz]

I take it this is PF ?

I think it would work in 3.5 - though I'm not completely sure - if that helps.

[LTwerewolf]

The extra damage is of the same type of damage as the strike that triggers said sneak attack. If the original strike doesn't qualify for sneak attack, no sneak attack happens.