I wish this was the reverse around... damn Game Freak
Honestly what you are attempting to to pull off here would probably take up to 2-3 turns as well as a considerable amount of prediction and unfortunately luck if Noivern doesn't get knocked up. I think the best way to pull this off is having a Trick Room Pokemon followed by a very "slow" U-Turner. Lets use Cresselia and Scizor for this as an example.
Method One: Trick Room
Turn one:
Opponent's two Pokemon go first (This is an absolute must)
Scizor gets off U-turn (needs to hit the Pokemon to switch out so predicting around protect the first turn is crucial)
------------Must be third to move before Trick Room goes.---------------
Scizor then switches to Noivern for a safe switch (with Focus Sash and Protect)
Cresselia (with Mental Herb) sets off Trick Room.
Turn Two:
Cresselia switches into Sylveon (hopefully taunt doesn't get fired onto this spot)
Noivern Protects
Sylveon needs to survive.
Turn Three:
Sylveon Skill Swaps into Noivern while it fires off a Pixilate Boomburst.
Method Two: Regular " Slow" U-Turn
Sylveon and Scizor lead
Turn one: Sylveon (Mental Herb to prevent Taunt) goes for Skill Swap at the Scizor spot while Scizor U-Turns out (must be the third pokemon to move) to get a safe switch for Noviern, which should then receive Pixilate.
That's probably the best I can think of since most of this requires having a good leads and setup opportunities.
Honestly what you are attempting to to pull off here would probably take up to 2-3 turns as well as a considerable amount of prediction and unfortunately luck if Noivern doesn't get knocked up. I think the best way to pull this off is having a Trick Room Pokemon followed by a very "slow" U-Turner. Lets use Cresselia and Scizor for this as an example.
Method One: Trick Room
Turn one:
Opponent's two Pokemon go first (This is an absolute must)
Scizor gets off U-turn (needs to hit the Pokemon to switch out so predicting around protect the first turn is crucial)
------------Must be third to move before Trick Room goes.---------------
Scizor then switches to Noivern for a safe switch (with Focus Sash and Protect)
Cresselia (with Mental Herb) sets off Trick Room.
Turn Two:
Cresselia switches into Sylveon (hopefully taunt doesn't get fired onto this spot)
Noivern Protects
Sylveon needs to survive.
Turn Three:
Sylveon Skill Swaps into Noivern while it fires off a Pixilate Boomburst.
Method Two: Regular " Slow" U-Turn
Sylveon and Scizor lead
Turn one: Sylveon (Mental Herb to prevent Taunt) goes for Skill Swap at the Scizor spot while Scizor U-Turns out (must be the third pokemon to move) to get a safe switch for Noviern, which should then receive Pixilate.
That's probably the best I can think of since most of this requires having a good leads and setup opportunities.