Is there anyway or work around to enjoy the dark mode feature of macOS Mojave without updating to it?
Briefly, no.

Why not install Mojave on a second drive (or just maintain a backup) so you can test things out with the new feature that shipped so you can revert as needed to your old system or data?

The framework and app updates to support this new feature are widely baked into the OS so you would need to have a poor excuse for dark mode by inverting the entire display using accessibility on High Sierra and lower.