I don't know if there is a way to actually shut a interface down based on routing. Maybe with TCL scripts but that is not your best solution.
Your problem is that you are learning about the main site via another remote site that you have connection to. Since it sounds like you never want to use this path you can use distribution lists to prevent the routes from being send/received.
I assume you have floating statics that you have not included that take over when the EIGRP routes are lost.
The cleanest way to do this is to go to this intermedite remote location and have it filter the routes it send to both the other location. It should be configured to not forward the routes it learns from these sites. You could do it as a inbound distribution on both the end routers if you prefer.
Another small point is the redistribute static statement you have will not do anything as you have it configured. You must specify a metric or use the default metric command.
Be careful about these redistributed routes. They will be advertised into the remote site that remains up. Since the statics only exist when the other links are down you may get unexpect results if our other location also is advertising the same networks. You will need to select your metrics carefully in some cases.
