I'm no engineer, I'm like a deer with no eyes when it comes programing but LMMS has "Sync VST Plugins to Host Playback" same with VSTHost , and they both have available source codes.

https://github.com/LMMS/lmms/issues/184
https://github.com/LMMS/lmms




I can slave another DAW running Kontakt, EZDrummer2, EZKeys, Temper, Wav Player VST's etc.. to RB with the Midi Out Clock and it works how it should with position and tempo but there is too much delay.