[ODE] Holding bodies like in HL2

[michael kapelko]

So I suppose ray collision detection happens only with a single geom (I 
can't find the second intersection, can I?). The ray goes from camera 
position (inside capsule) to the camera target. To make ray collide not 
with the capsule, but with other geoms, I should start it outside 
capsule. But how to find starting point which goes along needed vector 
and starts a bit farther than camera position?
Here's a picture of what I need [2K]: 
http://kornerr.users.kemcity.ru/pictures/ray.png
Thanks.