Joseph, secular civil law can override Halacha in two instances:
1. Commercial and labor laws have the status of minhag hamedina (Piskei Choshen, Dinei Halva’ah 2:29 note 82 and Hilchot Geneiva, chapter 1, note 4, p. 13 and Iggerot Moshe, Choshen Mishpat 1:72).
2. A takkana for the benefit of society which the bet din would have made if it had the power (Rama C.M. 73:14, Chatam Sofer Teshuvot Chatam Sofer C.M. 44, Teshuvot Imrei Yosher 2:252:2, Teshuvot Doveiv Meisharim 77, Iggerot Moshe C.M. 2:62) and Kitvei HaGaon Rav Y.E. Henkin 2:96 but see Shach C.M. 73:39 who disagrees).
While, of course, l’chatchila the litigation should be in a competent bet din if there are three frum Jews on the jury it might be muttar b’diavad as the litigants agreed to be judged by them. Whether a non-frum Jew can count as one of the “shepherds” is another question.