That saying was the inspiration behind making this thread.
Although I could imagine an isolated intellectual or two to become interested in Islam and convert, I'm having a hard time imagining a viable community of Muslim converts surviving for a long time during the Reformation. Perhaps in the United Provinces, with its relative tolerance of Jews, but even then, there's a difference in society's reaction between people born in another faith and remaining there and adherents of the "True Religion", even in its Catholic form, converting to Islam.
There was intellectuals who had a interest in Islam, and Islamic texts. Though I am not aware of anyone converting due to this more scholarly interest in theology. Martin Luther was among those who wished for the Quran to be published in Christian Europe. Though he argued in favor of this in order to refute it, and proclaim the superiority or truth of Christianity over Islam.
What may be more likely than a conversion to Islam, and founding of a Muslim community of converts in Europe is the founding of Christian denomination/sect inspired by it. This community would not self identify as Muslim, most likely they would still identify as Christian. Less likely in my opinion than identifying as Muslim or Christian is identifying as a new religion.
This denomination would draw people from the radical fringes of European Christianity.
Let's say that a community springs up of converts who see themselves as Muslims. This community may not be recognized as Muslims by the Islamic mainstream. Perhaps due to unorthodoxies in the denomination as a result of the Christian heritage of it's followers.
The existence of this community may be short, or perhaps likely to be short due to pressure put on it. Persecution could overtime kill or compel members to revert to mainstream Christianity. Alternatively, the members may be compelled or encouraged by pull/push factors to migrate into the Ottoman Empire. Settling in the Ottoman Balkans where they would be granted freedom to worship and perhaps free land.