this seems to be a uniquely vaishnavite concept. I don't recall Siva worshipers, Ganesa worshipers et al claiming that Gods they consider subordinate are Jivas.
Well they say.
For example, Devi Bhagavata Purana's Book 11, Chapter 18, gives the various methods of worshipping Goddess Bhagavati, by which one can attain the positions of several deities.
If anybody gives saffron, sandalpaste, musk, Sindûra and Âlaktak (red things), he will go to the Heavens and become there the Indra, the Lord of the Devas, in the next birth. Various flowers ought to be offered in S’rî Bhagavatî’s worship; or the flowers of the season offered to the Devî will lead the devotee to Kailâs’a. The devotee that offers the beautiful Bel leaves to the Devî never experiences anywhere pains and difficulties. The devotee who writes the Vîja mantra of Mâyâ “Hrîm Bhuvanes’varyai Namah” with red sandalpaste thrice on the tri-leaves of the Vilva tree leaf and offers this to the lotus feet of the Devî, becomes Manu by the merit of this virtuous act! The devotee becomes the Lord of the whole universe who worships the Devî Bhagavatî with ten millions of entire Vilva leaves, fresh, green and spotless. 24-40. If any devotee worships with ten millions of entire fresh green Kunda flowers, with eight scents, he gets surely the Prajâpatihood. The worship of the Devî with ten millions of Mallikâ and Mâlatî flowers besmeared with eight scents makes a man the four faced (Brahmâ); and one hundred millions of such flowers will make the devotee a Visnu. In days of yore, Visnu worshipped the Devî in the aforesaid way and so got His Visnuhood. If any devotee worships the Devî with one hundred Kotis of Mallikâ or Mâlatî flowers, the man becomes certainly Sutrâtmâ Hiranyagarbha. In ancient days Hiranyagarbha worshipped thus the Devî with great devotion and so he became Hiranyagarbha!