Not an "easy" way but not impossible if you're looking at individual posts rather than large volumes.

https://busy.org/@crokkon/what-is-the-reward-pool-share-of-vote-sellers-bid-bots-and-autovotes-1535479520399

The signatures of blockchain vote transactions can reveal who initiated the vote on behalf of the users. As a positive side effect: the same method also reveals autovotes via steemauto or steemdunk. The downside is: this approach is much more compute intensive and therefore slower than the bot list approach. Analyzing larger time ranges is costly.