How to Fade Tempo in or out?

I need to fade my tempo out to where it starts fast and gets slow(NOT Volume, TEMPO!). I have a track that says, “It’s about to go down!”, i need it to say," It’s about to go ddddddoooooowwwwwwwnnnnnnnnn". Is there an effect for this? If not is there software for this. Ive seen it done on radio stations, its similar to the cutting out of curse words.

Effect > Sliding Time Scale/Sliding Pitch.

or use a Time Track