Yes, it is possible. I'm too busy in other ways to figure out and write a full explanation, but here's a simple example.
In the .ssc file:
Then create a folder named "lua" in the song folder, and a file named "default.lua" in there.
The default.lua just has to return an ActorFrame with the actors that should be on the screen or whatever.
Simple example, just a spinning white quad:
InitCommand= cmd(sleep, 1000)
The Actor named "preserver" is there so the layer doesn't get unloaded.
This simfile has no real steps, it simply exists to show the example pasted above.