I'm planning on making a shake with frozen green tissue from a San Pedro Cactus. What's the best way of masking the taste so it could be easily consumed? Brown sugar, orange juice....?

The bitterness never goes away no matter what. The taste after all is part of the experience. I have had success with lemonade icees, this acomplishes two things one the acidic nature of the lemon seems to make it more potent some how and it does help soften the taste if you add about 1/3 more sugar. Make sure you use real lemonade from lemon juice just follw the directins on the bottle plus some extra sugar, you could also ues some mint leaves too.