You can summon creatures was th out a pre-existing creature (except the worker doing the reaction) without shack,but it's probably the most difficult thing in basic raw nodding. You need to have the interaction make a boulder that carries a syndrome that transforms the worker into a different creature temporarily and then the creature needs to have a body part melt off, but not die itself and then use necromancer on the melted body part to make it into a creature then have something turn the melted resurrected limb into a creature. That might not be it exactly, but the point is, it's really complicated and requires nodding pretty much every file type.
This is the method that Meph mentioned with the advice "But seriously, don't do that." I tried to do this before the spawnunit script emerged, and I concur with Meph. It's possible, but it's slow and unreliable.
What you want to do instead is find the spawnunit script and stick it in your raw/scripts folder (it's not yet stable enough to be distributed with DFHack). Experiment with a paused game running and typing
spawnunit commands into the console until you get the command line you actually want. Then you put the following line in
raw/onload.initmodtools/reaction-trigger -reactionName BUILD_GOLEM -command [ spawnunit parameters ]The parameters should probably include
\\LOCATION somewhere.
You can make the reaction require a statue as a reagent. Though not required, you should probably have the reaction create
some kind of product so that the Dwarf performing it gets experience. I used a boulder that boils away at room temperature to give a little "poof" effect.
Hopefully there is a functioning spawnunit script for this version of DFHack. I took an old version of warmist's script and stripped out all of the parts that gave me trouble. It works, but it's not general.
Now go back a couple steps. First you want to make sure the creature is working in the arena, and then make it naturally occurring and see if it behaves correctly in a fort.
Then take out its biomes and get fancy with spawning the things. You've picked a fairly ambitious project, but each step is do-able and it will be a valuable learning experience.