Don't urge others not to vote, but do some upvoting yourself!
I conjecture without proof that most upvotes to trivial solutions come from HNQ (hot network questions), who will be simply amazed at how short and concise golfing languages can be. The rest will be from people who never learned a golfing language, to whom the art of golfing languages seems worthy of an upvote.
Neither of these groups are put off by any banner (like the one I put in Community ads last year), comment (which can come off as hostile; since when is upvoting wrong?!), or line tucked somewhere in the challenge.
The SE model promises that through voting, good answers 'bubble to the top'. So, go out and vote! Specifically, upvote any answer you find fun and/or nontrivial (note the or, because sometimes, I find it amazing how trivially one can solve a task that by description seems extremely nontrivial).
Note: anyone looking at my profile will see that I am not living by my own words, as I vote very little. This is because I'm just a hobby programmer, and don't readily distinguish between trivial and nontrivial solutions, and possibly because I'm pathologically lazy.