Yes you can use a swc outside the lib's folder.
You must reference the SWC package in your project properties.
Rigth click on your project root's and go to "Properties" > Flex Generation path > Acces path > Add an SWC file > and select yourswc file.Click ok.
The compiler update and your SC in now ready to use!
I was not able to see Flex Generation path after clicking on the properties. I am flexbuilder 3