I know this is not the idea, but IOTL many "crypto-Jews" (forcebly converted to Christianity, but practicing their religion at home) went to Portugal at the end of the XV century, and later, to Brazil. After 1580, when Portugal And Brazil were united, and pressure against them in Brazil augmented, some of them fled to present day Argentina, Bolivia and Perú. In 1600, there were secret synagogues in Lima, who were uncovered by the Inquisition. Those who fled to Buenos Aires probably fared better, as there wasn't and inquisition tribunal, and nothing was heard of them.
Eventually, however, they were to few, and their descendants, at some point, stop practicing the faith of one or both parents (or maybe they chose to keep it secret from them).
There's a good historical novel about this, called
La Gesta del Marrano
Thanks, that might be an interesting novel to read (I've been reading into Argentine history in the past couple weeks. The 1810-1850 period is confusing as hell

. I get the Unitarian-Federalist divide, but the blizzard of coups is really hard to follow)
Anyway, I kind of knew crypto-Jews hung around Ibera for a while, especially Portugal...and, considering all the prejudice that was directed at Conversios (or however you spell it

), it doesn't seem
too far-fetched that Portugal, or a slightly more moderate Spain, might get the idea of packing them off to some isolated corner of the New World.
Say Ferdinand prevails upon Isabella not to expel Spain's Jewish population. Things, go, well, oppresively for them until Phillip II becomes king and, both being a good arch-Catholic and needing money, does order all Jews to convert or leave Spain without their property. Portugual thus gets a bunch of Jewish refugees it doesn't really want, and Phillip begins putting diplomatic pressure on the Portuguese crown to outlaw Judaism as well.
Portugal eventually does order all its Jews to convert, but, wanting settlers for southern Brazil, agrees to grant newly "converted" Jews land there with the promise that the inquisition won't bother them if they move across the ocean and out of royal sight (but not out of the royal tax register). Ultimately, 10,000-20,000 conversios are settled in a broad area of the coast, from Espirito Santo down to Rio Grand do Sul. All are nominally Catholic, but most continue to practice Judaism in secret.
This is somewhat controversial, and after the Portuguese-Spanish union, the Portuguese Inquistion gets turned loose on the place, generating a lot of fear and resentment and forcing the crypto-Jews deeper underground. In the early 1600's, the Dutch attack southern Brazil and find a good deal of support from the crypto-Jews, who, thanks to Dutch freedom of religion, don't have to be crypto anymore. Thanks to its established Jewish community, the colony becomes a magnate for crypto-Jews in the Spanish Empire, who immigrate in moderate numbers. In the early 19th century, it gradually secures autonomy from the Netherlands, and becomes a popular destination for Jewish immigrants from eastern Europe.