I have come to know that Glance screen is not available on the Nokia Lumia 520.
Is there some trick to get it working nonetheless? Preferably without compromising battery.
You cannot. Please follow the link to know why?
The Glance screen works without draining the battery too much due to the AMOLED screens. The Nokia Lumia 520/1/5 has a LCD screen, and thus is incompatible.
How it works is the Glance screen turns most of the pixels black. The AMOLED screens have the ability to turn off the pixels when they are black, so they aren't using battery by having the display turned on, unlike LCD screens.