The idea is just to do decent enough dps in dungeon settings while levling. I can live with it delay casting a bit here and there.

I want it to cast LavaB even if all shocks are on CD. <- I'll keep track of shock CD with a CD tracker to time this if needed.
If shocks are off CD I want it to cast FS first and then LavaB.

If not both of these are possible I will just have LavaB on a separate button and keep my filler cast button as it is.