Some devices allow you to connect an external antenna to your wireless device. If you can do this, that is the "Low hanging fruit" method I would recommend. There are many types of antennas so you will have to choose based on exactly how you would like to boost your performance. Typically most antennas in these types of devices are omnidirectional and that is usually appropriate under most circumstances. A directional antenna can provide a much stronger signal from a distance but requires alignment to the wireless device it is connecting to.
Another method you might try is to figure out where the receiver is on the USB device and fashion a parabolic focuser that will capture the signal and focus it on the receiver in a similar manner as a satellite dish or directv setup. The parabola need not be huge. You are just trying to create a reflector that collects EMI from the right direction and also reflects everything you transmit in the wrong direction back at the device you are trying to connect through.
Hope this helps.