For indulgence in any scripture of Hinduism one need not convert to Hinduism ever.
Hinduism is one such religion that is also called Sanatana Dharma, a Dharma existing from times immemorial. Hinduism is also called a way of life. Following precepts of spirituality detailed in Bhagavad Gita seekers like Mahavira, Gautama Buddha, Jesus Christ and Prophet Mohammed succeeded in reaching state of enlightenment.
Hinduism facts contained in Bhagavad Gita could never be belied by one world over. Everything contained in Bhagavad Gita was truth and only truth.
If anyone world over wanted to indulge in scriptures of Hinduism like Bhagavad Gita or Upanishads one could easily do it even while following ones religion, faith or belief. Apart from cultural bondages one is never required to convert to Hinduism.
Hinduism is primarily a very broad-based spiritual treatise consisting of Vedas (Hinduism revelations), above 200 Upanishads (independent spiritual treatises) of which 11 are primary, and finally the Bhagavad Gita, sacred teachings of Lord Krishna in the battle of Mahabharata.
I was born in Jainism religion yet from six years of age I believed more in teachings of Lord Krishna than precepts of spirituality detailed in Jainism scriptures. Here nothing in Jainism scriptures is being belied. The summation is everything contained in Bhagavad Gita was easier and simpler to understand, palatable even to commoners.
I equally believe scriptures of Hinduism and Jainism but to realize god in present life time I took refuge of scriptures of Hinduism the sacred Bhagavad Gita and Upanishads. There is nothing more pure, more logical straightforward than teachings of spirituality contained in Bhagavad Gita.
The 700 shlokas verses contained in Bhagavad Gita was pure gold, gems of spirituality. One single scripture Bhagavad Gita suffices for mankind to reach state of enlightenment.