I missed this, but looks like there is a way to interface second usb wlan dongle whit a cheap wifi router.
Recently searching for one open wifi book I found this : http://wiki.wndw.net/moin/DualRadioConstruction
On router running “Kamikaze” version of OpenWRT these gays are able to interface and compile drivers for ZyDas usb radio.
Here is a link to pdf file whit some pictures inside dual-radio-and-USB-ant.pdf
It will be interesting if there are possibility to use any of modern thing on the market to build something similar. The Netgear router used in this project is no longer available. As I know one of the little things whit a usb port are some of Asus routers, but there is broadcom not atheros radios inside.