P5, P6 and P7 can animate material parameters, so with the right node setup (to properly handle all aspects of the material i.e. specular and diffusein addition to transparency), you can make any material become fully transparent under the control of a dial (i.e. keyframable).
If you wanted to have more than one material under the control of a single dial you'd need to rig some ERC between the individual dials.