Rezzing a prim with a velocity relative to the Z axis?

I'm working on a fireworks display and apparently I've missed something basic I think. I can use the llRezObject to have it shoot the firework straight up, but I want the actual display system to be able to rotate at different angles to achieve different arcing effects with the trajectories of the fireworks. What I need is for the firing script to shoot the firework along the Z axis of the launcher prim which already has a rotation control script. Did I overlook something in the wiki under the llRezObject definition? or do I need to create some script that detects how much the launcher prim has rotated, extract a vector, and then apply that value to the velocity in the llRezObject command?

You need to get your velocity times the rotation of the launcher prim. That should project it in the right direction - as a velocity. You're looking at llGetRot and/or llGetLocalRot for the launcher angle, and it might be messy in a linked launcher system.