Craig - I've seen this usage in student writing quite a lot recently and I can't figure it out. Your example is really close to those I've read (I'll see if I can post a few from papers). And that I'm in New Jersey and you mentioned New York is striking. However, I haven't heard anyone speak this way, I've just found it in written form.

 

John

 

 

> I have seen a sudden increase in an awkward "in which" pattern, I think
coming out of New York City. "We were driving a car in which I bought
from my brother." That's not an actual example, so I may be distorting
the context, but in the cases I've seen, an unusual number, the "in" seems not at all appropriate. It does seem to come more from a spoken dialect.

> Craig