It looks like an armlike structure, the piece attached to the ETC looks like a joint, almost looking like a test version of the
feeler arm used on the Bv 143.
IMHO such a test setup seems more logical than a fixed launching device which on top is placed at an angle of the flight path.
The Bf 109T was still a small single engine fighter, probably ideally suited to test technology that was aimed at a naval cruise missile/glide bomb.
Actually unless I see a better explanation, I think I like my guess best
