Let the startup do what it does best -- problem solving
The beauty of working with a startup is that entrepreneurs think outside the box. The reason they start their companies is that they are passionate about finding a way to solve a specific consumer or business pain point. They dream about how to build a better mouse trap.
Take advantage of entrepreneurs' unique problem-solving skills. Outline a specific business challenge for your brand or client and ask them how they would solve it leveraging their teams and technologies. Be sure to keep an open mind and don't be trapped by your preconceived ideas about how this should work. Listen to what they say and ask for details about execution if it sounds too good to be true. Even if you don't end up with a partnership, you'll reap the reward of some great new thinking.