In my personal experience, and from watching others, the lock-in and absorption in your work comes with a succession of tasks and exertion, towards a meditation of sorts. You don't simply "fall in" to this state, but rather makes a concerted effort in reaching it.

> is it something you must be born with?

A motivation to reach this state, to keep trying and pursuing it, may be a fact of your nature. Or, it is an understanding of what your work will create. Fame, money, fulfillment – extrinsic motivators that drive you towards a definitive conclusion.

To meditate in your work might just require you to find your motivator.