We demonstrate experimentally that the spectral broadening of CW supercontinuum can be controlled by using photonic crystal fibers with two zero-dispersion wavelengths pumped by an Yb fiber laser at 1064 nm. The spectrum is bounded by two dispersive waves whose spectral location depends on the two zero-dispersion wavelengths of the fiber. The bandwidth of the generated spectrum and the spectral power density may thus be tailored for particular applications, such as high-resolution optical coherence tomography or optical spectroscopy.