In RealTrack Prefs, there is a checkbox to Enable RTs. Uncheck it and no RTs will play - only the Midi parts.

My other suggestion may give you better results as long as the RT generates RealCharts (as Richard noted). If you want to try it, generate the RT and copy it to another part such as the Soloist. Mute the RT and assign the part to the desired Midi instrument. I've had good results with piano RTs.

R