There are plently of “non spiritual” yoga classes all over the place. In fact, I would say most are wellness based and have no mention of any ties to religion.
You could try Spira yoga in the Admiral (Valerie and Dora are amazing)
Or the new gym formerly known as All Star has some great classes.
Venturing out of WS, Brenna Hindman teaches at Community Fitness and she is nothing short of wonderful.
I have been practicing yoga for most of my life and would say that I rarely find a practice that makes me feel like I am being preached to; I always feel stronger and more relaxed after.