Building on the previous posts, it's easy to see how you can implement functionality in ICE that isn't there natively. One example is the limitation of the ID to Location node - it only works for particle IDs and not geometry indices.
The tree below constructs object context arrays of point locations and their indices. From then on, whatever context you're in you have access to these arrays and can query the location of any other index on the mesh. The only slight twist is that you need to use 'Find in Array' as lists of locations can't be conventionally sorted.