(So that it extends through the whole channel depth and stands perpendicular to the flow path). It is desired that the channel has a transparent window for optical visualization.
Perhaps, If you create some defects (for instance: pillars) on PDMS and you let dry your rods on it. Most of the rods will be align between two pillars. After you spin coat a thin layer of PDMS onto the structure to encapsulate the rods. finaly you bound your channel (PDMS again) perpendicularly to the rods. I think it can work!