The Piano Roll Editor tool has a module called ChordBuilder, which allows you to quickly build chords to shoot them from a single key. In addition, it allows routing to specific tracks and specific instruments, without moving from the selected track or instrument in Renoise. It is probably the best tool currently for these things. You can try it and judge for yourself.
The ChordBuilder works with the PRE’s superior mirror piano. It is only necessary to assign the keys of that piano to a channel of the MIDI input in order to use the ChordBuilder. Precisely, the next version of the PRE will bring significant improvements to the ChordBuilder, related to routing. It can even be converted into a “Battery/Drum Rack” of up to 120 pads to route directly on up to 16 tracks. Or play / record with the left hand chords from a single key on the current track and, at the same time, play / record complex melodies with the right hand on another track directly. Probably no exist a tool or VSTi that gives you more control than that (apart from the piano roll).