Void Masters.SetSpeed(Handle handle, Single value)
another example in http://forum.avolites.com/viewtopic.php?f=20&t=5731:
This sets the value the fader is currently set to (in Playback Options). If the fader is currently set to BPM then the bpm rate is set. If the master is currently set to 'Multiplier on Fader' then the multiplier is set.