I am not sure, but it might be possible to put a nail in the center of the ceiling where you want the center of the web to go, and then tie a string to the nail, paint it and then carefully stretch it to the edge of the room and push it down so that the paint goes onto the ceiling, and repeat for everywhere that you want a line going outward…. Then use smaller pieces of painted string to make the circling lines. Not sure if it would work or not… would probably take two people. But maybe that will spark an even better idea for how to get it done!
What made me think of it is — sometime in art, if you want to make a reference line that won’t stay, you can cover a string with powdered chalk, stretch it between two points, and then lift it up so that it kindof slaps down on the surface, and it gives you a nice straight chalk line… and spiderwebs have mostly straight lines that connect from one part to another. Best of luck with your project!