While typing this my mind went through 3 plausible solutions but the final more plausible would be to consider splitting the primary image on your imaging scope and use one as a guide.
This would though be based on whether or not the image can be split and whether the comet can be bright enough for the guide software to see it. I do know that there is some software that can split windows images into 2 streams. I do not know how effective it is but should be possible.
My 2 bobs worth
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