Kant writes in Groundwork for the Metaphysics of Morals (page 46)
If, then, there is supposed to be a supreme practical principle, and in regard to the human will a categorical imperative, then it must be such from the representation of that which, being necessarily an end for everyone because it is an end in itself, constitutes an objective principle of the will, hence can serve as a universal practical law. The ground of this principle is: Rational nature exists as end in itself.
He then states the imperative: (page 46-7)
The practical imperative will thus be the following: Act so that you use humanity, as much in your own person as in the person of every other, always at the same time as end and never merely as means.
From this one sees that being treated as an end does not preclude one from also being treated as a means.
The OP asks regarding a Creator who creates to fulfill its nature:
Could an almighty Creator make something that was an end in itself?
Following Kant's use of ends and means in the above imperative, that the creation is a means to fulfill the Creator's nature does not preclude the Creator from also using the creation as an end in itself.
Kant, I. Groundwork for the Metaphysics of Morals. Translator Allen W. Wood. Retrieved on June 27, 2019 from Internet Archive at https://archive.org/details/KantGroundworkForTheMetaphysicsOfMoralsWithEssays/page/n64