One simple rule is to gather the whole team and brainstorm for a day, ways to growth hack the new product/feature. Try to make sure everyone has some ideas to spread before writing code or creating mockups.
Because of this discussion, the team will have growth hacks in the back of their mind while building the new stuff. When it is their in the back of the mind, they will find a way to accommodate the "product" hacks.
Most of the times, these hacks are left to be implemented during the last stage of development and they get dropped because implementing them will mean you need to change a lot of already created code/design which is difficult to achieve.