Well, I was a little bit too fast with asking this question. I did a little browsing through the Neat code, and apparently using
padding: flex-gutter();
works.
Does anyone know if this has any downsides?
Edit: Well, I found the downside. flex-gutter(), or using the bourbon function pad () (same result except for padding), defines the padding/margin around 2.3%. Problem is that, when you'll view your grid on a large screen, the padding will get huge (while the gutter on your grid holds on to a maximum of 25px.
So I kinda made my own max-margin:
margin-bottom: 25px;
@media (max-width: 1100px) { margin-bottom: flex-gutter();}
First line defines the max margin, the second line sets flex-gutter if your viewport is < 1100px (my max grid size for Neat).
Would love to hear if I can implement this in a sass function!