Build a crazy jig for the pins to ride against.
Set the template stock against the jig boards such that both pins bear against the jig boards. Feed it thru left to right, keeping pins in contact with jig boards until the pin on the other end approaches the router bit. Don't route the pins off!
Viola! A true radius routed in the template. The footboard arch is a different radius that this one. The set-up is almost exactly the same: one jig board has to be swung "open" a bit, but it will result in a radius of something like 18 feet. That would be a really, really, really big circle jig.
