I’m not sure if it’s still possible to do this, but I know people, including friends and colleagues, who got their student DNI by doing a degree at the Universidad del Tango and they only had to attend classes once a week (theoretical classes mostly, because they were doing something like History of Tango). Classes were in Spanish though, and this was a few years ago so I’m not sure if it’s still possible.
As for Spanish classes, a few years ago CUI (Centro Universitario de Idiomas) were the only language school that was “requirente”, i.e. that could process student visas for their courses. They got all the Chinese students because of that, so all the other language schools were complaining because they wanted them too. I don’t know if this is still the case (this was 10 years ago), but you might want to look into it.
As for Spanish classes, a few years ago CUI (Centro Universitario de Idiomas) were the only language school that was “requirente”, i.e. that could process student visas for their courses. They got all the Chinese students because of that, so all the other language schools were complaining because they wanted them too. I don’t know if this is still the case (this was 10 years ago), but you might want to look into it.