creating environments in package's C code

Dear developers,

is it possible to create environments in C code of packages?
Simply using
SEXP env;
PROTECT (env  = allocSExp(ENVSXP));
and assigning the enclosing environment with SET_ENCLOS seems to be  
insufficient.

Rf_NewEnvironment is the function that does it, e.g.,
Rf_NewEnvironment(R_NilValue, R_NilValue, parent)
it's not part of the official API (headers) but it is visible.
For hashed environments it's R_NewHashedEnv().

Cheers,
Simon