OK, as it turns out, I did not explain my question very well at all. here is a complete re-write.
I have Xcode 4/iOS SDK 6.1 installed. I want to install and use Xcode 5 but want to use iOS6.1 SDK. I know that I can download iOS6.1 SDK from Xcode 5. But, I want to avoid that since the iOS 6.1 is already in my hard drive. Is there any way I can avoid having to download iOS6.1 SDK again.