How do I get more money out of my boss when I know the company is spread thin already?

Try and negotiate some benefits other than pay raises like longer vacations, more flexible work hours, company stock, and increased health benefits are sometimes negotiable.

Date him

The way to get more money while helping your company to survive is to be as productive as possible and ensure your boss knows you are indispensible. Your boss should be thinking to himself/herself, "I have to do everything possible to ensure xxxx doesn't leave!"

Theft.