To dynamically load a procedural, we can add a Dynamic Load Procedural node in the shop/. 

In order for it to work, we need to also add Min/Max Bounds. 

In your geometry node, set the Procedural Shader to this procedural shop node.

Another way is by adding a ri_objectpostinclude or ri_worldpostinclude appropriately.  Then type in exactly how you want it to appear in the RIB, e.g.  DynamicLoad" ["F3DProcPrim" "{test.f3d} {density}"] [-1 1 -1 1 -1 1]