in this case you are going to need to use two or more methods to work this out
1) identify your beats and put in kicks or similar markers at each point (on a new channel/track) - then use auto-tempo on that track to work out the tempo if possible
2) identify your beats as above, then use the accuracy of the timer to identify time between each pair beats and calculate a tempo on per beat basis
2 might be the better path as the first will be an average tempo whereas 2 wuillgive you beat accurate tempos
I like to play the acapella track, tap the tempo and get as close as possible. Then, I'll play the track again with the metronome running and fine tune. Hope this helps!