I was think of revising the AT-ST for a mod, thought the cruise missile-type launcher was a little extreme for a medium-sized walker (which we could probably throw into the "light tank" category).
However, after playing a little Mercenaries 2 and Battlefeild 3 I realized a missile that works like the TOW/ATGM would be perfect for an AT-ST.

After fiddling around with ODFs I cant get anything thats not either a fire-and-forget, or a chase-screen missile.

Is such a weapon possible?

You can try work on the com_weap_award_rocket_launcher and see what you get.

I tryed that and all I got was chase-screen