If you have two free VCAs, a triangle LFO and an inverter you can patch a crossfade between two of the waveforms.
Send each waveform into one of the VCAs, and the outputs of the VCAs into your mixer.
Send the triangle LFO (sine will also work, but I prefer triangle) into the CV input for one of the VCAs. Now, invert the LFO signal and send that to the CV of the other VCA. The speed of your LFO will be the rate of modulation between the two waveforms, so a VCLFO will give you another dimension of modulation in your patch.
~Terry