This technique has actually been done before. I've seen it performed by Orbit Concepts' very own Wil (DJ Stress) way back before Serato was introduced to the DJ world. Here is what A-Trak have to say about this technique:
"I had this idea for a new way to switch tempos in a set - say you're at 100 and you want to go to 70. That Skepta song is at 70 but on 45 it's 100-ish. Say I'm coming out of a song at 100, I can then scratch a little beat with the intro of the next one I want to play (in this case Skepta) as an interlude, and bring it down to regular speed and play the song at 70. #RealDJing"