Yes there is.
But due to the limited reach of USB you'll probably want to (or need to) use a USB over Ethernet extender. http://www.maplin.co.uk/usb-cat5-booster-221290
That one isn't USB 2.0 so will be limited to 11Mbps data rate which is probably about 3~6Mbps maximum. That might be enough for 3G for now but not future-proof for new dongles.
*** I don't see why this wouldn't work, but I have never tried this. ***
You'd need to put the dongle in a weather proof box. A drinks bottle would do the trick upside down with the hole where the cable comes in through the lid sealed up with silicone sealant.
You're not adding an antenna you're just moving the dongle to outside where the signal is better.
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