It would definitely be feasible to make an aluminum form on a CNC lathe, or better yet using the Tormach mill as a vertical lathe. This form would them be dipped into liquid silicone rubber as many times as you want to create the desired thickness. My Renishaw probes have quite thin rubber boots with very good flexibility to prevent restricting any movement of the stylus. This is not a difficult project but it does require knowing what the required shape for the rubber boot should be for a specific probe. I can provide numbers for the TP1A, which is what my three (actually, now two since I gave one to a friend) probes are.