That is not possible, and I would assume this is by design. It goes against the spirit of this kind of DAW. It is derived from early sound synthesis software that were designed around systems where the sound generation was done at the hardware level, and the hardware didn't have the circuits to allow a single instrument to play multiple tones at once. Instead, you have to cleverly split notes for an instrument across multiple channels. How you do that is up to you, but one simple approach is to just alternate between two channels in a "zig-zag" pattern.