The only method I've ever heard of that allows you to forgo performing a reboot is through the use of the KSplice technology.
What is Ksplice Uptrack?
Ksplice Uptrack lets you apply 100% of the important kernel security updates released by your Linux vendor without rebooting.
Ksplice Uptrack is available for Oracle Linux, free of charge, for Oracle Linux customers with a Premier support subscription. Additionally, anyone can use Ksplice Uptrack for free on Ubuntu Desktop and Fedora.
According to the website it's free for Fedora and Ubuntu Desktop users:
Free for Fedora and Ubuntu Desktop.
History of technology
The KSplice technology came on the scene in 2009, if memory serves me correct. The impressive demo the technology developers used was to migrate a Linux system through all of the Linux Kernels that were ever released. I never saw the demo but that claim has stuck in my mind ever since.
Here's the Ars Technica article that I remember reading, titled: Ksplice: Update computers without rebooting.
Lastly here's the technical paper that covers the technology and how it works, titled: Ksplice: Automatic Rebootless Kernel Updates.