Your use case which necessitates to change the split dynamically is quite specific. Perhaps you could try the split Scriptlet in this rackspace:
It could be that I took into account the possibility to change the splits dynamically. I don’t remember well… please try and let me know.
Just a little trick. When you are in a gig file where you find an interesting Scriptlet, you can simply select the Scriptlet and define it as a favorite. This way when you are in another gig file and need it too there, you can simply add it as a favorite.