Since all the 4.1.0 update + ss stories are making me sad, here we go:
BIG FAT WARNING: I don't have a K4, so this was dry-coded, and, more importantly, *UNTESTED*. It might very well not work, or worse, break something. Make sure you're ready/able to play with the diagnostics mode/debricking.
You'll need a
jailbroken K4, of course, and it'll need to be clear of any previous SS/Fonts hack, and as always, not a KSO device. And freshly rebooted, to avoid weird issues.
The screensavers hack is probably way safer than the Fonts hack, which I anyway strongly recommend you *NOT* use, because I have no idea how it will interact with the KF8 stuff/the browser, and it's way more intrusive than the ScreenSavers hack, so, yeah....
On the bright side, I remember
seaniko7 packaging these for the K4 a while ago, so there's hope that it actually does work

.
If it is deemed safe enough, this'll eventually move to the first post with the rest, but in the meantime, consider it alpha untested crap.

.
EDIT: The ScreenSavers hack has been moved to the front page (with proper K4/K5 binaries). The Fonts hack package here has also been updated to use proper K4/K5 binaries.
EDITē: The Fonts hack is now out of beta, too. Moved to the front page.