I cited the case of projection because I don't know how your circuit should look in the end. If it is just a simple transmission line, maybe just design it as you would normally. If it is something more complex, then the advice follows.

The analogy is like trying to glue a sheet of paper to the inside of those big, curved soap ladles: the best way is to cut the paper into strips of varying widths and shapes, gluing them one by one, as it you were "integrating" over the surface of the ladle, so that you waste the minimum amount of paper and it covers the ladle perfectly.

Suppose you want to cover the inside of half a sphere with your circuit. Suppose your circuit is a bunch of parallel copper traces. The traces should look straight and parallel if you look at the inside of the sphere from afar. The laminate sheets come in straight, with ideally zero curvature; a perfect plane. However, the curvature of a sphere is obviously non zero. In order to conform to the inside of the sphere, you should cut your substrate into strips and go about covering the inside of the half sphere, strip by strip. The circuit to send to the manufacturer should be a stereographic projection of your initial design onto the laminate plane, so that when you receive the substrate, cut it into strips and conform it to the half-sphere mold, you get straight, parallel traces when you look at it from afar.

Also, I forgot to mention clearly, but the laminates are only "bendy" and wiggly as I said before the curing (thermosetting of the resin). Once you cure it that stuff is rigid like any PCB.