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Wouldn't it necessitate only one sock puppet account. It could be seen negatively to upvote its own comment this way but it still could be done.

At this point I tend to disagree with this solution and I'm still unsure about the course of actions that should be taken.

I agree with @teamsteem, the creation of just one sock-puppet account is an almost negligibly small discomfort to the average (ab)user. That's why my own algorithms have always treated self-votes and sock-puppet-votes the same.