I know Milwaukee well; I visit frequently. This is definitely possible. Choice of clematis (or clematises - a mixture might be nice) depends on how far away the root zone of the clematis is from what you'd like to cover. Also, since you're near the beach, are we talking full sun and sandy soil? Or full sun and garden soil? If you send me a private message I can probably help you out (Minors has a decent clematis collection, for instance).

But to cover an area like what I'm picturing, you might want 2-4 clematis for width. Type 3's that you cut back each spring, ones that grow fast and with little care. Also, the rocks won't be too hot for the vines as long as the roots get adequate moisture. Ones like sweet autumn clematis come to mind, also Prince Charles, Etoile Violet, Emilia Plater, Hagley Hybrid, Bonanza, Jackmanii.

You could also try a a variety of integrifolias that can cascade down the area. How about also something like X jouiniana praecox or even types like Mrs. Robert Brydon?

The rocks would actually provide a shelter for the roots. In my area, there are local colonies of wild viorna plants that grow out of the rip rap rocks that are placed along a slope to prevent erosion. The southern heat reflecting off the plants doesn't seem to hurt them.