Hi Generator,
Although I don't use software, I know that on drum machines there is a button called "tap". When you hit tap a few times it matches to the tempo you tapped in. So you can hook up into a mixer and listen to a song from another source (cd, multitrack etc.), and then punch a drum loop or programmed beat from the drum machine on the beat of the song and, it will display on the drum machine what bpm it is. This is much easier to do when working with electronic music with programmed drum machines.
So, I'm thinking it will be a function in software called "tap", or something saying bpm/tempo, that will do this for you. Maybe it's in software that you already have.
Even the metronome. You could record the song into the sequencer and then turn on the metronome, and try to match it up by adjusting it till it fits.
I'm sure somebody else here will know for sure. I'm just sharing what I know from using hardware.
I hope you find out soon...
evt