It’ll be tough because you would need a dedicated PCIe x4 bus and above. I’m not sure many of these low power CPU would support that on top of supporting a SATA bus. Zimaboard has a PCIe expansion slot but it’s limited to 6.0 Gbps (guessing they use the rest of the bandwidth for something else like storage).

You can increase your bandwidth if you have a multiple NIC computer though. You can tie in 2X 2.5Gbps to get about 4 Gbps to your switch.

Edit: assuming you mean 25G and not 2.5G?