Force Play Tag

[Fritz]

Ground ball to 1B who fumbles the ball toward the bag as he is running to tag the base. Grabs the ball securely with his bare hand and reaches back to touch the base with his glove hand.

Safe or out?

We've been debating this all afternoon. I say out as he touched the base with his body (though covered with the glove but don't consider that much different than touching it with his foot encased in a show). Some others say safe because the glove isn't part of your body.

Haven't been able to find a great rule reference or case play that discusses this.