It seems no one has ever released a plugin that can do this (at least not the full source code) so I decided to make one. It's not perfect, but at least it is good enough to add a simple entity to portal 2.
As well as adding entities, this plugin also adds 2 console commands:
-
dump_full_datadesc {entity name} - dumps all save restore variables and keyvalues
-
read_datadesc_val {entity name} {value} - reads a single datadesc value from an entity
This only works with the 2014 build of portal 2 with PDB debug symbols.