Well, I don't deem this impossible, but all I got is the beginning for sure. well atleast kinda: ;D
_rocket = "laserguidedbomb" camCreate [(getPos _target select 0) -2000 * (sin(getDir _target)),(getPos _obj select 1) - 2000 * (cos(getDir _target),(getPos _target select 2) + 10]
_rocket setVelocity [300*(sin(getDir _target)),300*(cos(getDir _target)),50]
Theoretically that could be a start heh. The LGB would be the only realistic "missile" sadly, as it'll tip over and such when dropped. Nothing new there but what follows that creation would be the corrections to its flight path. All relative to the _target. You should be able to control it well enough with setVelocity.
Apply that velocity again in a slowish loop, with the [(300 *(sin(getDir _target)) ... it might just work setting it's new heading again. When (_rocket distance _target) < 50 move to a faster loop so it really works harder to hitting it.
Add a smoke trace script for some realism...
And you'll need a loop to check the target, hmm that will be harder but very possible.
* MI_Fred shrugs
I'll give that a go later.