Slide 5 in Jason's link shows that you have to click on Solution, then the Write Input File will not be grey.

One way I know how to use line bodies that lie randomly within a solid volume as reinforcements is in the Explicit Dynamics solver where the Body Interactions tab allows the line bodies to be called out as type = Reinforcement.

This is rather elegant. The line bodies are meshed independently of the mesh of the solid volume. It is the solver that figures out which nodes of the line body is inside an element of the solid body, and connects those nodes to the intersecting solid elements.  Below is a bit of the ANSYS help section. Reinforcement Type

This body interaction type is used to apply discrete reinforcement to solid bodies. All line bodies scoped to the object will be flagged as potential discrete reinforcing bodies in the solver. On initialization of the solver, all elements of the line bodies scoped to the object which are contained within any solid body in the model will be converted to discrete reinforcement. Elements which lie outside all volume bodies will remain as standard line body elements.

The implicit solver used in Static Structural has a different way of dealing with reinforcement. I recall making sure the line body mesh shared nodes with the solid body mesh. Maybe some one else will comment on other methods available.