You can use actionkey in the prelude to bind extra keyboard keys to object spawning. When a bound key is pressed, the bound object is created on every player tile, then one turn of rules is processed.
Use one line per binding:
actionkey <key> <object>
You can define multiple lines to support multiple keys:
actionkey c crystal
actionkey v vine
actionkey f fire
If action keys are enabled, the default control hint updates automatically. For example, if you bind c and v, the title hint becomes X,C,V to action.