This Ableton tutorial shows how to use the MPE Control device inside an Instrument Rack to route MPE expression data into instruments that don't natively support MPE, using Operator as the example.
By default, an MPE controller sends Pressure, Slide, and Note Pitch-bend data, but non-MPE instruments like Operator simply ignore it. The fix is a hidden routing section inside the MPE Control device, revealed by activating three checkboxes in the bottom right corner.
Those checkboxes map Pressure to aftertouch, Slide to the mod wheel, and Note Pitch-bend to pitch-bend. Once enabled, any parameters already assigned to those standard controls in the instrument will respond to your MPE input, making expressive per-note control available across virtually any Live instrument.