Cantennas are wave guide antennas made from cans, that can boost wifi range up to a mile. The most popular ones are designed using Pringles potato chip cans. The advantage of using this type of antenna is they are small and easy to handle and set-up in public areas.
There is some drawbacks with using this type of system. The passive element design requires a RF cable between the antenna and the wifi card. The maximum effective length of this cable is 18 inches. Cables longer than 18 inches start to lose the signal strength that was gained by the cantenna. Also, the type of cable required for the connection is more susceptible to failure from fatigue.
From all of the designs linked to on this page, I would suggest modifing the PVC one to accept a USB WiFi device by cutting a slot (where the pigtail is installed) large enough to insert the USB device. Then make the washer/rod eliment depicted in the picture above.
Below are links and demos on how to make and use one..
Links Here