I'm going to assume that you're talking about in NL, and I'm also going to assume that you're speaking of a parallel loading dock system instead of a co-linear system. If either of those assumptions is false, then sorry.
In NL, you won't be able to acheive this effect with actual track, but you can construct a secondary route through a custom station (which I would suggest building in this situation anyhow because path routing is much different) using steel support pieces to simulate the track. This technique is used by a lot of people right now to create transfer track (used in parallel stations as well!) and maintenance branchs/extra train storage.
Of course, there *might* be some sneaky way to get NL 1.6 to do this for you that I'm not aware of, but as far as my knowledge goes there is no way for you to actually construct a free-floating piece of extra track.