AutoCAD .NET :: Replace All 3D Polylines With Cylinders

I'm trying to automate a simple yet massively tedious task at the moment. Certain layers of my drawings contain 3D Polylines that have to be converted to cylinders. What I need to do is select all 3D Polylines in a specific layer and automatically convert them to cylinders, these cylinders will all share the same hardcoded diameter, however will retain the x,y,z, positioning of the 3D Polylines. The way that I'm approaching i'm attempting right now is to use a selection filter to select all 3D Polylines, save their co-ordinates into an array, create the cylinders using these co-ordinates and then deleting the existing polylines.