Modalys-ER is a graphical environment for creating physical model instruments and generating musical sounds with them. While Modalys-ER provides users with a relatively simple-to-use interface, it has only limited methods for mapping control data onto model parameters for performance. While these are sufficient for many interesting applications, they do not bridge the gap from high-level specifications such as MIDI files or Standard Western Notation (SWN) down to low-level parameters within the physical model. With this issue in mind, a part of Modalys-ER has now been ported to OpenMusic, providing a platform for developing more sophisticated automation and control systems that can be specified through OpenMusic's visual programming interface. An overview of the MfOM library is presented and illustrated with several musical examples using some early mapping designs. Also, some of the issues relating to building and controlling virtual instruments are discussed and future directions for research in this area are suggested. The first release is now available via the IRCAM Software Forum.