The rule is that non-gradable adjectives like unique cannot accept modifiers. However, that doesn't mean that educated, erudite native English speakers don't do it often. Everyone has a unique narrative style, but the phrase very unique conveys to me a meaning that is distinctly different from plain unique.
If something is nearly invisible or almost impossible it means it is visible or possible. Yet we say that the bird's nest was nearly invisible in the tree top, and it is almost impossible to go downtown without running into a traffic jam and these things make perfect sense to us.
My advice would be to avoid using modifiers with non-gradable adjectives unless it is absolutely unavoidable (as opposed to just plain unavoidable).
Remember the famous words of Homer (Simpson, that is) "You are unique...just like everyone else."
- For Teachers