Okay. Whoa.
The toilet you are looking at, you realize, requires an in-wall tank. You know that, right?
If you have an in-wall tank already, then it's already going to be configured to work with whatever Duravit or Toto wall-mounted bowl it was installed with. And your bowl is designed to work with the two major in-wall tank systems. So it would just replace the Toto or Duravit bowl that is already there.
But a 4" rough-in, meaning that the centerline of the waste pipe is 4" above the finished floor, suggests to me that the thing is designed for a floor-mount, rear-outlet toilet like this one:
That setup is relatively-rare these days, and sadly your choices are somewhat limited.
I am guessing that if your building won't let you open the wall to move the rough-in, they're not going to let you open the wall to install an in-wall tank, either.
If you want us to point you to some floor-mount rear-discharge toilets, we can do so, if that is what's there and that is what you are looking for. The choices are sadly limited and the aesthetics are also limited.
There is the Geberit Monolith (street price, $600-700 without the bowl), which mounts in front of the existing wall to let you install an "in-wall" tank in front of the wall without opening the wall, but I fear that you still might have an issue connecting to the waste pipe.
And if you're going that route, give up on the snobby, overpriced Gilleroy & Bosch stuff, and buy something that works, like a Toto Aquia wall-hung (Model CT418F) or one of the various Duravit wall-hungs. But, again, I think you have some work and expense ahead if you want to install those without opening the wall and without an existing in-wall tank.
