In that case, look for people outside the companies that you work with, e.g., someone senior in a major client company or in a company you partner with. The idea is to find someone who is (a) observes your work and knows you professionally and (b) can speak objectively about you.
Also, in an optional essay, briefly explain who the recommender is and why you chose him or her.
Senior Advisor, Accepted
Follow Accepted on Twitter
Friend Accepted on Facebook
Subscribe to Accepted's Blog