I've used Japanese matcha tea powder in a cake. It has a lovely taste.
The taste is really spring gras green tea, very fresh. The Japanese themselves use it a lot in pastry. It is expensive though when you buy a good quality.
It pairs good with white chocolate, pear.. passion fruit..
I've used it as well as a natural food colouring in my marzipan, wich turned out beautiful.
When you use to much you get the taste of grass, wich is not so..
Try a teaspoon first.
I am afraid just green tea won't work. I am not sure though. You can use just so little of a liquid in BC. I don't now if you will be able to get the flavour strong enough. When you make a reduction over fire it will probable get too bitter.. But I didn't try myself.