Hi Tim. I would recommend you touch base with Joseph Ramadei. Joe recently left Chadbourne & Parke in New York to join Boston's Gennari Aronson. He specializes in working with startups and early stage companies, and he'd be happy to discuss flexible payment or whatever suits your needs.
I don't have his Gennari email address, but you can reach him at firstname.lastname@example.org.
I hope this is helpful. Joe is brilliant and I'm sorry he's leaving New York!