i was thinking of

1. acurately mark out on both sides, the center of the styrofoam square.
2. using a circle cutting jig on the bangsaw, cut the foam down to 1/2 less dia than 700c(it would have to be an outfeed jig even the largest bandsaws dont have enough space to cut down something thats 700c)
3. using a bullnose router bit on the routertable cut a half round profile along the outer edge of the foam disc.
4. using appropriate jigs, tacking methods, glue, etc attach clincher/tubular rim to the outer profile of the disc
5. carve out hole on disc surface with forstener bit. the hole should be towards the outer diameter for the valve
6. bore second hole using the center points marked out earlier. this is where the hub will go.
7. mark a line directly across from the valvestem and hole. mount the hub and disc on truing stand. this is where you might have to possibly add some weight/balast to keep the wheel balanced. (this may or may not be a step)
9. using a sureform rasp, shape styrofoam disc. the idea is to creat a gradual and natural line from the outerflange of the hub down to the endge of your mounted rim. a hot wire could be used, but some modification to the device might have to occur so as not to create inaccurate or awkward cuts because of the hub body and its relation to the rest of the rim. there is the possiblity of creating your own jig where the known dimensions of the hub body are used to create a device/set up where a truing stand and hot wire are used together to create the desired profile.
10. finish with 80? grit paper
11. lay up carbon/kevlar in layers. be sure to minimize overlapping layers so as not to throw the wheel out of balance. be sure to bleed the layers properly

yadda yadda.
the hardest part is acuracy. you COULD just lay up some carbon but will it be safe? will it ride like ****?