I can't.

I am hopelessly bad at controlling the life energy I share with any target.

It should work in theory, but in practice, it will definitely fail.

No matter what the target is made out of

when it gains more life energy than it can hold, it will surely turn gigantic.

In the case of human beings, their limbs and necks will stretch abnormally, their eyes and tongues will become bigger than their faces, and the internal organs will expand to the point of bursting through the body or wrapping the whole body around.

And if that happens, I won't be able to undo it.

If I pour my life energy into an inorganic object and turn it into a gigantic living being, I can return it back to its original state by taking back my Stand power, but...

a gigantic creature created by me pouring my life energy into a living being won't revert back even if I take back my Stand power.

In other words,

If I fail and pour too much life energy into Bucciarati...

Bucciarati will have to live with that disgusting appearance for the rest of his life.