The short answer is that you can't, if by 'budget' you mean that you plan to know exactly what you're going to spend on it and reduce the amount of time/energy/money you plan to spend on collaborative excitement if you need that time to do other things.

But what you can do is to plan and make space for it in your project - make sure that the time is there for brainstorming and excitement and creativity. If you do that then the energy you create will help the budget problem take care of itself.