I've never been too interested in flavoring it as I believe the distinct flavor is part of the experience (and the price we must pay). I also love the idea of this seemingly magical liquid that tastes like something that could kill you, but makes you feel amazing instead.
However, I've been doing an Aluball for 1st wash and blender method for 2nd wash and have been putting a tsp of black seed oil into the blender. I started taking the black seed oil bc of derm, (which I do think it helps with) and because the fat in it potentiates the effects for me. It's one of those "miracle" health oils that extra crunchy granola moms swear by and is mentioned in the Bible, etc. But it also has this earthy taste along the same spectrum of flavors you'd find in Middle Eastern cooking (it's from that region) like nutmeg and clove. It actually pairs really well with the kava and can make it almost pleasant in a non-artificial way. It also gives it that coffee with cream look instead of mud when blended. You do have to buy good black seed oil, I've found. Lulu naturals is usually the kind I get on amazon for $29/bottle. I've tried with cheaper brands and the flavor has been poor. I guess kava has given me expensive taste now.