As said in the title, I don't think that this is possible because recipes unlocked are stored within the research prototype, and not the recipe prototype.

The best solution i can think of would be a function like

function addToFluidHandling(recipeName)
table.insert(data.raw["technology"]["fluid-handling"].effects,
{
type = "unlock-recipe",
recipe = recipeName
}
)
end

I haven't been able to find a way. What you have is essentially what I'm doing with the latest release -- all cube versions of all fluid-based recipes are unlocked when fluid-handling is unlocked.

I might just update the mod to replace the existing recipes with the cube versions, which would preserve the tech trees. Thoughts?

RE v 1.0.2
suggest if possible make the fluid cubes optional otherwise you must make the cubes for all fluids before you can use them, adding a step and always costing iron plates

another option would be to have the cubes not cost iron plates and be generated by any entities that makes fluids so instead of pipe you use belts and inserters for all fluids

EDIT: looks like v1.0.1 doesn't switch every recipe and you can use either the cubes or not, will try this version out instead, but will still have to make cubes for any fluids i want cubed, it would be nice if the cubes were generated by the fluid entities tho.