Latency compensation in Ardour with Jack Dummy-Backend

[robin]

Hi!
Inspired by
https://github.com/ponderworthy/MultiJACK
I am trying to seperate Jack-Instances, one for Low-Latency monitoring with plugins loaded by Carla, and one "I dont care about latency" instance for recording and on the fly mixing with Ardour. Each instance comes with a different buffer size and they are connected by zita-njbridge. I have a working setup as follows:

Hardware Jack Server, ALSA backend 48*2 samples, ~6ms roundtrip latency
Dummy Jack Server, Dummy Backend, 384*2 Samples, ~47ms roundtrip through the whole chain, including the Zita-Bridges and Hardware

Basically, it works as intended, its easy on the hardware but provides good latency for monitoring. The problem is I can not inform the Dummy-Jack about the additional latency (no -I or -O swiitch in dummy-mode), so Ardour cant compensate for it. I recorded the metronome through the whole chain and I get misaligned recordings by around 26ms, which corresponds to the additional latency by zita (2*10ms for in/out) plus 6ms coming from the Hardware-Jack, at least thats what I assume.

Is there any way I can tell Jack in Dummy mode, or Ardour directly about the additional latency caused by zita and the other Jack?
Thanks in advance for any thoughts!