This behavior is a great annoyance to me - I find it incredibly egregious.
How about a sign that says something like, "If you plan to hover, please lift the seat first so that it stays clean and dry for others." Evil doodlemor can think of many things to post, but they are not within the realm of polite.
I mean, really--men stand to urinate into toilets, right? In places where there aren't urinals.
And we expect them to *lift the seat* out of the way, right?
I want those signs to say, "When men stand to urinate, they lift the seat so it doesn't get pee splatters on the top. If you plan to not sit, please be a gentleman, and lift the seat."
As for the OP's situation, I'd vote for plain English on the sign. And put one in every stall.
"Recently we've discovered that someone is peeing on the seat. If you are someone who does not want to sit on the actual toilet seat, please lift it out of the way so that you do not splatter urine on it."
As for fragrance-free--what about rubbing alcohol or bleach? Are there bleach wipes you could make available?