Translation:Вареники, будь ласка.
The primary word for "please" I learned growing up was прошу. I understand that the language has changed from the 1940s Galician that my grandparents knew but I've talked to many Ukrainians and they still understand me which leads me to believe that it can be an acceptable answer even if you don't want to teach it in the lessons. Duolingo is also providing a service to allow 3rd and 4th generation ukies from immigrant backgrounds to talk with their relatives and friends in the Ukrainian diaspora as much as for those who want to visit Ukraine. Just saying.
I agree. Ukrainian-Canadians would almost unanimously say this as "пироги, прошу" instead of "вареники, будь ласка".
Well, at the very least they'll understand it because Poland is next door and that's the Polish word in most common use for that purpose.
Others (such as, presumably, you) are more knowledgeable than I and may better comment on its validity as a "true Ukrainian option".
In any case, if you do want a word adding, you just need to use the "report" feature :)