Some opinions and proposals regarding this:
As far as I know a "stage.def" doesn't usually have or can't have the complexity and flexibility that any .cns file has.
While the programming of a character has a large series of commands that allow you to create algorithms, variables and decision structures that you want, "stage.def" can only configure the position of the fighters, positioning and animation of "stage.sff" and some basic effects. And parallax.
In this case I have two possible solutions to this problem:
1 - If "stage.def" has support for the commands used in .cns files just program in "stage.def" as if you did with any .cns. Then it would be enough to save and test to see if the effects work.
2 - If "stage.def" does not support the commands used in .cns files, the solution seems to be to create a "stage.cns" file, program it normally and make the "stage. def" to read and require this file to work.
@ELECTRO, @crosspotts1.0 recommended you for that matter and now I call you to check if this idea is plausible.