iOS Stacks or equivalent functionality
- Long press any app icon to enter "wiggle mode".
- Drag the desired folder to the Dock.
- Press the Home button to exit "wiggle mode".
Done!
Not through folders, no, but if you're JailBroken, there're a couple tweaks in Cydia that you can get called Infinidock and Cascade. They're $1.99 and $0.99, respectively. When you put them together, it adds an Overflow type of look to your dock. It's close to what you're asking, but other than that, there isn't anything that does what you want.