We present an experimental C interface to Oz, which enables programmers to add metaterms to the DFKI Oz system in a modular way. Low-level issues, as garbage collection and waking up suspended computation, are transparent. Metaterms are fully compatible with the other components of the system, as for example the Oz Browser. Metaterms are a well-suited means to implement instances of the clpx(X) framework. To demonstrate the use of the interface we implement a solver for clp(Real Intervals).