Tom:

First I would give them a history of yoga. What its original purpose, who practiced it etc. . .

Second I would point out to the person what is biblical meditation versus eastern meditation. This is going to require some research on your part. Then compare what these CY practitioners say for meditation and see how closely it matches to eastern meditation practices.

Lastly there is no easy answers to this any more your going to have to combat both post modernism as well as poor theology. So your going to have to do the research.

Peter

If you believe what you like in the gospels, and reject what you don't like, it is not the gospel you believe, but yourself. Augustine of Hippo