Like the Acer Aspire One, there’s also a 40-pin ZIF connector (unused here) compatible with most 1.8″ PATA hard drives, and there’s a missing mini PCIe connector and SIM holder on the motherboard for 3G.
I went ahead and temporarily connected 1.8″ PATA hard drive to the ZIF connector. The thin (5 mm) hard drive fits in a dedicated opening in the bottom casing of the Eee, but requires the removal of the 8 GB mini PCIe SSD. This worked fine, but the 4 GB mini PCIe SSD became the IDE slave device.
Next I connected the 8 GB SSD from my Acer Aspire One to the ZIF connector, and kept the 8 GB mini PCIe SSD in place. Once again, the 4 GB mini PCIe SSD became the IDE slave device, but the existing 8 GB mini PCEi SSD was disabled…
I hope this info is useful to some people out there!