If you know what tempo changes you might require in a song then you can make them in BIAB standalone. For instance you might have verses at one tempo and chorus slightly faster then back to normal verse tempo and maybe a different tempo for the bridge. Maybe you might want a gradual slow at the end you can do all this in bar settings. Once you have all the tempos as you would like them you can export the song as a midifile into your DAW. This song will include all the correct tempo changes. Now when you export your RealTracks or RealDrums from BIAB to your newly created DAW song they should all line up perfectly with the tempos.