I can't seem to find a manual for the unit (the website doesn't properly link to the "Manual&Download" section from the header, and the "Support Center" link doesn't do anything at all), and since it doesn't mention anything about a WiFi antenna adapter, it's hard to say one way or another with any level of confidence.
That said, it may be possible. It seems to contradict itself in a couple of places referring to a "WiFi/3G/Mic Cable" before later calling it a "3G/USB Cable+Mic Cable". The "3G" actually requires an external modem to function, so I'm guessing it's just two USB ports. It will probably accept a USB WiFi device, but it's questionable if the OS will support the hardware. It does have a built-in WiFi modem, but I'm not aware of any USB antennae designed to connect to a separate device.
NOTE: IF YOU FOLLOW THE SUGGESTIONS BELOW, IT MAY A. VOID YOUR WARRANTY AND B. BRICK/RUIN YOUR DEVICE. PROCEED AT YOUR OWN RISK, I ACCEPT NO RESPONSIBILITY
If you were to open up the case, it may be possible to find a place to connect an antenna to that built-in adapter. If that's the case, you can probably get an extension cable that would let you then place a long-range antenna somewhere more appropriate. I know my Samsung Galaxy S4 has two little connectors for external antennas, but I don't think either is for WiFi.