Hi all,

I think you can already do this in BIAB. Try this and see if it works...
Start a new song then from the menu bar select File --> Open Audio and load your audio file. Because it is an audio file the style will be disabled. When you hit Play you can then use the tempo up/down buttons to change the speed of the playback...the pitch remains the same. If you know the tempo of the song before hand you can set it before loading the song so it'll pretty much match the audio file.

Does this work for you?