You might want to post in the Surgery forum? But, Neurosurg is a very small field and I would expect most (if not all) applicants have some sort of neurosurgery research background before applying for residency. It's also a useful way to make meaningful connections with physicians in your home department.
I'd definitely talk to a physician in your home department about this. You could do something simple (i.e. clinical research and/or case reports, etc.). A lot of these are small studies you can work on at home (even as a 3rd year) with an existing data set.