Your question basically here is: How to do penance now (in Kali Yuga) without dying?
Then the answer is it is not possible to do Tapasya now like it was used to be done in the earlier Yugas (specially in Satya Yuga).
Even in Treta Yuga, Tapasya was not the ideal way. Knowledge (Jnanam) was. Tapas was the suited way only for Satya Yuga. In Kali Yuga it is charity alone.
See the following verse from Manu Smriti:
1.86. In the Krita age the chief (virtue) is declared to be (the performance of) austerities, in the Treta (divine) knowledge, in the
Dvapara (the performance of) sacrifices, in the Kali liberality alone
And, the reason why it is not possible because in Kali Yuga people depend on the food for their existence. So, fasting (without which Tapasya is not possible) is not suited for us specially if it's for many days.
In the Satya, Treta, and Dvapara Ages, the Mantras, O Kalika! were in
their application preceded by the Pranava (9); but in the Kali Age, O
Supreme Devi! the decree of Shangkara is that man do perform all rites
with the aid of the same Mantras, but preceded by the Maya Vija (10).
All Mantras in the Nigamas, Agamas, Tantras, Sanghitas and Vedas, have
been spoken by Me. Their employment, however, varies according to the
Ages (11). For the benefit of men of the Kali Age, men bereft of
energy and dependent for existence on the food they eat, the Kula
doctrine, O Auspicious One! is given (12)
Mahanirvana tantra's 9th chapter