Source audio track set up with "send" to harmony track with harmony VST enable on the receiving track - set Harmony VST to 100% wet, set harmony/receive track to record and press play. This should record the incoming harmony which can then be spliced & diced as required though it's possible there'll be a tiny bit of latency.
OR set up as above and instead of record select the harmony track, then select freeze render...it'll do it in machine time and should have less lag.

Cheers
rayc
"What's so funny about peace, love & understanding?" - N.Lowe