Im pretty sure they sampled the vocal and then made it a midi track. But I don't know how they put it in the right key (maybe melodyne) and elongated them. (Also might be melodyne) This is a good technique whatever these guys are doing. Any input will help.

(the sample is pretty much the whole beat in this one)
http://soundcloud.com/theodorfresco/uhh-girl

(the part im talking about comes in at .58 seconds)
http://soundcloud.com/cashmerecat/withme

 

i did almost the same here at 2:33 :

http://soundcloud.com/mrlyannmusic/r3hab-nervo-ummet-ozcan-1

how i did it :

- Load your Vocal Sample into Newtone, change all the notes to C ( not sure how i did it but, Ctrl+A then double click the C4/C5 it depends on the vocal sample's octave).

- Then load the sample into Edison.

- search for a good part, then copy/past into a new Edison or clear the one you're working with.

- Declick in/out (Normalize it if you want(it's an option)).

- load it into a sampler or put it into step sequencer.

- play with your midi file.

PS i'm using FL Studio as main Daw so i don't know how you're gonna do it with another Daw, but i gave you the basics.

Hope i could Help !

PS : on the preview you posted, he did the procedure more than once!

 

ok im gonna give it a whirl i use fl studio too *yes*