VIA EPIA-M and two port riser?

Anyone know what's involved in getting Via's two port PCI riser (which
supposedly makes use of special features in the VIA BIOS) working under
linuxbios? As it stands I don't get an IRQ assigned to whatever's in the
top slot, so I'm assuming it's not working as of now.

Is it as simple as adding the missing pci_assign_irqs for device 0x13?