Reducing Hops

The title is a little rough, but really covers the gist of what I am trying to do. Let me explain.

I work in a building with two businesses. Business "A" is an online service provider, business "B" consumes the services of business "A". I do IT for both businesses.

Both businesses, although sharing the same building, are hooked up with different ISP's. The latency between the businesses is a bit sub-par, as the closest exchange between the ISP's is about 300 miles away in a different state. I would like to attempt to increase the bandwidth and decrease latency between these businesses, because its silly to have to send traffic on a 600 mile round trip when the two businesses literally share a building.

Both businesses have fairly high end routers. Business "A" has a Ubiquity "Edge" router, the other has a Ubiquity "Dream Machine Pro." Each router has a spare WAN port to dedicate to this endevor.

I can run a CAT6 cable between the two easy enough. My question is two part:

1) If I want to send traffic from B to the public IP of A, do I just create a static route from B to A on the shared interface?

2) On the "A" router, do I just assign the public IP to that interface as well? This way I have two WAN interfaces with the same "public" address?

To reiterate because I had some trouble explaining on another forum, I am not attempting to connect the LAN side of each network. Each network will be completely isolated and firewalled. I just want to reduce the hops between the WAN facing sides of each router.