Thanks for your Question!
I think, delayed power uptime would only solve this problem for exchanges, but we need to expect that this can also happen from individuals and also if they split the votepower on many accounts this probably would be under the radar.
Voters either need to be identified or trusted. I would prefer the latter.
Ya, it seems once it gets down into many smaller accounts this would definitely be harder to track unless the voting behavior was identical/unanimous and same times etc.