A two-week independent project is always a better fit.
A techie doing a code and design review after that project is done and delivered would be a perfect follow-up. They can talk about design decision, coding practices, algorithms etc.
A techie doing a straight interview is a no-no. In this era of multiple platforms, languages, libraries, frameworks:
{set of techie 'interviewer' questions} and {set of potential founder knowledge required for success} is almost an empty set.
Sure you can ask basic fundamental CS questions of algorithms and data structures or threads or map-reduce or nosql or javascript or rails and test their knowledge. But, none of those are predictors of success.
For a startup, the best predictor is execution. Why not do a real world test of execution?
So, you are on the right path. Just follow it up with a design/code review with a techie.