We’ve in the past separated out specific components that people wanted to be able to exclude without needing recompilation (such as ARToolKit, which has the restrictive GPL license), but there hasn’t been much clamour to make this happen with Cg in specific.
Although we certainly do plan to make the Cg support a loadable plugin that can be removed at runtime, for now, you’ll need to compile Panda3D from source. It isn’t difficult to do so, however; it’s simply a matter of installing the right packages followed by invoking “makepanda”.
It can be argued that recompiling Panda3D with --no-nvidiacg falls under “easily excluded from the installation”, but I admit that it’s worded a bit ambiguously. However, I am planning to overhaul the shader system to be slightly more modular, which will give me the opportunity to separate out the Cg support as a separate, loadable module, similar to how we separate out the FMOD audio plugin and ARToolKit. Can’t give any promises about when that will happen, though.