just taking time for browsing the SDK, ignoring the fact that I'm writing an exam tomorrow ...
nothing really useful found, but some stuff which looks promising
//-----------------------------------------------------------------------------
// Purpose: Interface to get at server entities
//-----------------------------------------------------------------------------
class IServerGameEnts{ ...
sounds nice, especially there is a function to get a BaseEntity pointer of an edict_t *. the BaseEntity class in the HL2 dll itself looks that it's rather basic for other stuff, and won't be hopefully changed by a mod ( otherwise this won't be much of object orientation ) ...
virtual CBaseEntity* EdictToBaseEntity( edict_t *pEdict ) = 0;
unfortunately I havnt yet figured out how to load that interface. with that CBaseENtity, we'd get origin and stuff.
Edit : I think I got how to load that interface ... please stand by 
another edit :
in the serverplugin_bot.cpp, I added
IServerGameEnts *servergameents = NULL; // for accessing the server game entities
then I loaded the library by putting
servergameents = (IServerGameEnts*)interfaceFactory(INTERFACEVERSIO N_SERVERGAMEENTS, NULL)
into the load function of the plugin ... and now I gotta see if I can load that plugin at all by HL2