For any interested in a way to use a wall mounted sprayer on an exterior wall, this was our workaround. Had a local metalworker make the stainless backsplash for behind the sink to mount the faucet to. All of the plumbing is still "inside" the house (no plumbing inside the wall).

The sprayer is a Krowne 17-109WL and the sink is a Whitehaus WH3018. Got the sink from bluebath.com (found them via Gardenweb). Can't remember exactly where we ordered the sprayer from.

You may notice that there is a height difference from the stainless backsplash and the countertops. My intent is to (eventually) make concrete countertops and I had the stainless made to that future height. The countertops a just laminate. The installer did put strips of solid surface countertop under the laminate along the edges of the sink to prolong the life of the countertops in a wet area. He wanted to make sure I knew that laminate countertops and an undermount farm sink don't match - which I understood. I figured once the countertop started to delaminate, that would prompt me to make the concrete countertops. He said with the addition of the solid-surface strips, it should last a long time.

I used clear silicone to seal around the sink.