I'd be tempted to figure out a way to add at packaging or even serving the first time to experiment with amounts.
If you don't already have the bark I suggest getting quinine extract which is just extract of chinchona bark. I got some last summer because I was sick of HFCS in tonic water and wanted to make my own less sweet tonic for G&T's. Maybe you could get a similar style commercial beer and add a drop to get a sense of the taste. And seriously, a drop. Its a strong taste and getting it right will be tricky. If you have the bark you could make your own tincture and try something similar.
I like the idea, i hope it works.