[chrisbennet]

If the technical person is not making an "investment" [in uncompensated time] they sound like an employee. I would think that equity for an employee should be enough that they want to stick around.

That said, don't expect "co-founder" performance from an employee. If you think you need the technical person to be as committed as you are, you should align their goals with yours i.e. make them a co-founder.