Solution: Disable voting on the top comment(s). This would allow the trailing comments to catch up until they are the top comments and their voting is disabled. The top comment can't race far ahead of the others.
Now I'm oversimplifying, but the effect would be that comment 1 and 2 swapped place over and over again. Or the first N + 1 comments, if you restrict voting on the first N comments. (And people might be confused, perhaps annoyed, when they cannot vote on the first N comments?)
This would not help promoting [a really good but forgotten comment] that is located far away at position 10 or 20.
The submission ranking, I assume, takes more into account than just upvotes (age, number and quality of sub-comments, etc). The top-comment problem feels like the same problem, so might be an opportunity for code consolidation.