Not knowing the industry your SaaS is targeting perhaps you could take the route that the original founders of Reddit did and lie to the first few businesses that come onboard. http://venturebeat.com/2012/06/22/reddit-fake-users/

Get all your friends to sign up to the service and interact with the first 10 or so business customers as if they were real users. You don't have to go free open beta for the first 6 months to verify the MVP, you could even confirm the idea by visiting or cold calling some of the target businesses you're interested in poaching. Perhaps try to stick a high dollar price on the monthly rate and offer the service to the first 10 signups for free or generate interest with an awesome landing page and a big closed beta image to procure email addresses from both users and businesses..