Quote from Worgslarg
If you are on a singleplayer world, you could use mcedit.
Never used mcedit so I'd need to get familiar with it. It's easier for me to just recreate the spell on the inscription table and make it and then delete the items from my inventory.
Still, couldn't hurt to look at mcedit anyway. I've a feeling this essence-fed-spell-creation is never going to work for me.