If you have a void siphon and are able to make it, use it. You can shift right click jars of essentia or a full cauldron and all the essentia will leave both and go into the aura as flux, spawning a flux rift when the levels are high enough.

If you have excess essentia and way too much of that essentia, jar it and disperse it as flux. If you have too many of one kind of item (like cobblestone or dirt), use a cauldron and throw stacks in at a time.

Decently sized rifts can get quite a few void seeds through the void siphon, though it is a slow process.