If that city can build transport ships, you might want to do that. Ferry the units to near that city, unload them, and then load them on the other transport ship. Kinda weak workaround, but it would do almost the same thing. Just take longer.
Edit: Actually might not take that much longer if you unload them in a port, and are connected by railroads to each port. But you'd still have to have double the transports to ferry them where you'd want to go.