I know nothing about LIVE, but in any program you should have a tap tempo feature of some sort.
Something that automatically sets tempo like beat detective probably souldnt work because the transients of words shifts more than a music instrument like drums which stay pretty steady through a song.
If you use a tap tempo feature or whatever its called in LIVE while the vocal is playing, you will figure out its approximate tempo. Then you should be able to begin editing the length of the entire region/ clip, and then sit it in properly with the tempo.
To do a Tap Tempo, youd simply listen to the flow of the verse and tap the designated key at a 4/4 time signature. like 1,2,3,4 1,2,3,4