Hi. We are having an outreach learners service and after our nei’la service we’ll be having a break-fast. What is the earliest a non-Jew can begin preparing for a Jew on Yom Kippur (for breaking the fast)? Can a non-Jew set up, etc. for a Jew during Bein Hashmashos (as a shevus d’shvus b’makom tzorech)?
It might be a little too late for the answer, but it appears that one can be lenient for a non-Jew to perform non-melachos during bein ha-shmashos in preparation for after Yom Kippur.
See Peri Megadim 503 (Eshel Avraham 1) who mentions a doubt concerning hachanah by means of a non-Jew, and the Maharsham, who is lenient concerning this matter. Although the Shulchan Aruch Ha-Rav (319) is stringent on the question, there is certainly room for leniency during bein ha-shmashos, which adds another safek to the equasion.
This is in addition to the idea of shvus de-shvus, as mentioned in the question, which is permitted for purposes of a mitzvah.