Upgrade to iOS 5 with iOS 4 blobs?

I have an iPhone 4, which has the original factory iOS 4.0 I'd like to upgrade to 5.1.1 for an untethered jb. I know if I restore in iTunes, it wont get signed and it will only work to upgrade to iOS 6. I wondered if there was any way I could stitch my iOS 4 blobs onto the iOS 5 fw, and do it that way? The only reason I ask is because I notice the latest RedSn0w allows iPad 2 users to use iOS 4 blobs with iOS 5 fw...