I started a topic on this same idea about a year ago. There was some interest, but it did not progress from there.
My recommendation is to stick with PHD2 for comet tracking mode. You can get the dRa and dDec rates calculated from www.minorplanetcenter.net/iau/MPEph/MPEph.html
You will want to choose these options:
Ephemeris interval: Hours (especially for fast moving comets)
Separate R.A. and Decl. sky motions
Display motion as: "/hr
When the HTML tables are generated you will be interested in the values under Sky Motion.
Ensure Sticky lock position of OFF in PHD2. Because eventually the guide star will be lost, and a new one will have to be selected elsewhere.

Carte du Ciel can also calculate and send the rates to PHD2 and is INDI compatible.
It certainly would be nice if EKOS could make the same ephemerides calculations and send the values to PHD2 and internal guider as well.

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