how to update an iPhone 4S from iOS6 to iOS7 but skip iOS8

Hi all,

I would like to update to iOS7 on my iPhone 4S because many app now require it. However, I believe iOS8 will be too heavy on the hardware. I tried to save shsh blobs, but Redsn0w says it's not supported, tiny umbrella does not work, iFetch neither.

Any hint?

Thanks!
F