This is technically a two-for-one deal, however the premise should be easy to grasp. Bonus content: 'Royal Knight's Resolve' off-hand casting. It's simple, casting it on your main hand weapon buffs anything in your off-hand without expunging the effect... even spells.
But this should be short and sweet for those looking to get a little more bang for their incantation buck.
Edit: (RKR offhand has now been patched)

So we'll get right into it.
https://gfycat.com/craftycautiouscirriped

Video above is with only 50 faith!

The basic premise is that we're using the spell 'Bestial Sling' and move queuing in order to glitch our casting animation on the next adjacent spell in our memory slots.
Spells that I've found to be 100% consistent are the Lightning ones, specifically: Honed Bolt and Lightning strike. However I have gotten it to work with a few others including self-buffs but it's too inconsistent to be worth posting, but I highly encourage experimenting yourself.

Like I said, short and sweet, but if I'm remiss of anything please do let me know.

Haven't seen anyone post or talk about this so I might be among the first to encounter this atrocity — great for dealing with curse-abusers at a distance. Genie's out of the bottle now but I kindly ask to refrain from using it while invading. New players have enough on their plates already when trying to co-op.