You can get switches that have RGMII interfaces for external PHYs on some or all ports, and it is entirely possible to run this to your cards rather then ethernet (This part has ports 7 and 8 set up this way, so if you can live with just two slots having ethernet then you can run RGMII or such (4 bits each way, 125MHz DDR, which should be fine).
That way you only need the magnetics on the external ports, not on the ports connected to the on card MACs.
There are ways to use capacitive coupling instead of the transformers, but setting up the DC bias can be a pain depending on the details of the pin drivers.
73 Dan.