I was also thinking of Hirany Garbam as a process where one enters thru the mouth of a golden cow and comes out thru the rear. It is said that there is no re-birth, once u do this. Yes there r inscriptional evidences for RRC n Danthi Sakthi Vidangi doing this at Thiruvisalur.
The extra gold that was remaining after making the golden cow was used for the Thiruvalanchuzhi Kshethrabalar!
But, when I googled for 'Hiranyagarbham', what I saw has amazed me. Am posting some of them:
Hiranyagarbha is the cosmic germ, the world soul, the third in the hierarchy, who is identified as Brahma. The followers of Vishnu believe that Brahman was born from His umbilical chord, as they consider Him to be the Supreme Brahman Himself.
The Rigvedic perception of 'Prana' and 'Bhuta' - the life and the matter, which the Rigveda calls Hiranyagarbha is explicit and better defined. In the Hiranyagarbha analogy, 'hiranya' or gold is the 'Prana', the life and 'garbha' the 'Bhuta', the matter. The Rigveda observes that it was the single egg but split into two - the 'Prana' and 'Bhuta'. The Rigveda does not elaborate the point any farther but its symbolism moves into two apparent directions. Egg contains both, the life and the matter. When it splits, both fall apart. Besides the lifeless matter, the Egg also yields the matter with life. The Rigveda calls them as 'aprana' and 'saprana'. The matter with life has life but is just the single Egg, the inherent aspect of the female, as by itself it is unable to farther the creative process and it is thus only the inactive 'Bhuta'. It is only after the male energy fertilizes it that it becomes the Golden Egg- the life-bearing one, the Hiranyagarbha of the Rigveda. And, now the Hiranyagarbha- the 'Bhuta' combined with 'Prana', the matter energized by spirit, takes to its own form and defines creation.
Vishnu Sahasra Namam Jagadaadijah - One who had born (Jah) in the very beginning (aadi) of the world (jagat) is called Jagadaadijah. At the time of dissolution (Pralaya) when the entire gross and subtle bodies go to lie absorbed in the Total Causal-body, the world, in Pralaya, lies merged in Eesvara. Before the gross world-of-plurality emerges out there should be a condition of subtle manifestation of it in the form of thoughts. Thoughts constitute the mind-intellect; when the Infinite functions through this Total Mind-intellect, It is called as Hiranyagarba the womb of all objects, it is from the Hiranya garba-state, the manifestation of the gross world emerges out, when the lord comes to play as a Virat Aatmaa. Maha Vishnu is the one who was born before the world of gross bodies, therefore it is indicated here that he is the "Womb-of all- objects" in the world, the Hiranyagarba-the very creator.
On his death bed, Chatrapathi Shivaji is reported to have asked his assistants to to let him touch (or tie his hands to) the tail of a cow . He wanted his soul to hold the tail, enter the womb of the cow and get sanctified before further journey. Madan narrates this in 'Vandhaargal Vendraargal'.