The same way you would when employed by any other type of business.
The other distinction is that we have no dedicated HR staff so I'll be negotiating directly with the CFO.
Just go ahead and ask. If they tell you there's no money, or that they think they're already paying you enough, try to negotiate a re-evaluation in 3 to 6 months.
Decide for yourself if you can live with not getting a raise. Negotiating directly with the CFO beats negotiating with him through an HR person.