A way to approximate - I emphasize 'approximate' - is to:
1) . . . host Pianoteq in a sequencing/synth ap/program for example, Logic.
2) . . . set your chosen Pianoteq preset to have a minimum polyphony such as 2 or 3
3) . . . chose your synth preset from the host ap/program with polyphony of 12 or more
Either my suggestion AND any other way that might be technically more to your liking would require a carefully executed playing technique. To be thinking about these type of things is akin to the automation organ manufacturers went through from early Lowrey Organ Co.'s AOC (Automatic Orchestra Control) of the 1960's up to present auto accompaniment technologies for playing in real time. Layering tracks with state of the art synth devices is fine. But keyboards that let you "sound like a pro" as you are playing in real time require that players actually know what they are doing in the first place!
Lanny