It seems to me that you're making a very common mistake and using "help support" to mean "get a kid to learn what I want them to learn". In essence, you're getting stuck between the ideas of teaching and learning. That's normal for someone new to unschooling! So many of the cultural messages about children are that they need to be "gotten" to learn what we want them to learn or they'll go bad in some way. The whole field of child development has been suborned into education, and that's a massive mistake because learning - always, always, always - comes down to the learner, to their thoughts and feelings, the direction of their attention and interest, their assumptions and perspectives and the unique quirks of their personal development. Unschooling begins with the assumption that all those things matter more and affect learning more than adult desires for kids to learn the right things at the right times
What that means on a nuts and bolts level is that fretting over neurological development and reward centers will distract you from getting to know your child as a person. You're focusing on who your kid could or should be, rather than connecting with them, right now, as they are. That's also normal! As parents, we're wired to project a whole lot onto our kids. A substantial part of the deschooling process for parents is about overcoming that natural tendency to see our kids as extensions of ourselves.
One reason that matters (again, on a nuts and bolts level - I'm not talking about ethics or respect or the human spirit, here, but about unschooling as a purely utilitarian practice) is because human beings are wired to be social animals. People learn from other people. So building a warm, personable relationship with your child increases the likelihood that they will be interested in and value your thoughts and feelings and goals. On the most cold blooded level, unschooling works by manipulating probabilities - but the patterns of probabilities we're talking about are also exactly the kind human beings best understand in social terms. It's Easier, as a human being, to focus on social relationships than to be endlessly doing the math and tracking the neurological pathways. In social terms, that means it's also "more authentic" - actually building a warm, communicative relationship with your kid "feels better" on both sides than being a robot manipulating another robot.
So.. back to delayed gratification. It's developmental. You know that. That means you can't hurry it along - you really can't "help support their development" in that sense. But you can get in the way, and ironically the best way to do that is to try and get kids to delay gratification when they're not ready for it. That makes them frustrated and sets them up to want to avoid it, in the shorter term. In the longer term, because children are egocentric, it seems to them that adults get to demand what they want Right Now (come here! put that down! look at me!) while kids are expected to stop and wait, which builds an expectation of future entitlement based on the power to demand - when I'm big, I'll get to have my way. It will be My Turn to demand. That's actually a recurrent theme in discussions of deschooling - learning to let go of that sense of entitlement and use our adult powers of delayed gratification where kids are concerned.
On a day to day, practical level, that means that, rather than setting kids up to wait when they really aren't wired to do it yet, to think ahead, see things from their perspective, and actively look for ways to help them out. Set things up so they don't have to wait so much. Offer lots of distraction and comfort and reassurance when waiting is inevitable. Being the grownup by letting little kids be as they are, developmentally and as a function of their individual personalities and temperaments.
And it works! Unschooled teens and adults are not grasping, impatient, entitled brats. At worst, they're people, with human failings and foibles. Unschooling isn't a cure for humanity. It's an agreement to work with our kids humanity rather than against it. And it absolutely does work.