a non-technical cofounder could have a deep understanding of the market dynamics and users the company wishes to serve. This includes pricing tactics as and strategy, channel development, scaling a non technical team.

They could help develop the long term strategy for the company ...what are the 5,6,20th features the company will sell etc?

edit: also, they can build the skillsite necessary to develop and test business hypothesis. this might be the most important this they do early on.