I've got an Edimax EW-7711MAC and tried all the said on the first post and it still without working. When I copy the Kext to its folder, I've got an error message that tells me "The system extension /System/Library/Extensions/RT2870USBWirelessDriver.kext doesn't installed properly, so It can't be used. Try reinstall or contact with the manufacturer"Any ideas? According with Edimax, till late January, there will be no Yosemite driver.
you have to fix permissions too, just copying wouldn't work.
Instead, download Kext Wizard and install kexts using that.