Once they talk about adding a SATA controller- imho, trimode controllers become the obvious solution.

If you want to get super hacky, if the SATA backplane is direct instead of multiplexed, passing a single lane of PCIe over SATA is possible. Probably limited to pcie 2.0 though. And they're absolute abominations, real frankensteins monster stuff.

Edit: I mean the physical layer. Obviously you can't control a pcie device with a sata controller, but the cable will do a single wide pcie link.