You can just supply your own function to parse the date.

In most database systems that would be a disaster, because the database would have a send a request over the network back to your program for each argument it needs to process. For SQLite, it's no big deal, because it's executing in the same address space as your program so it's a simple function call.

I'll admit that it does make it harder to port your program to another language, so it's more of a workaround than an ideal solution.

How would do that easily?

Did you mean writing a c extension of Sqlite?