I know there is a way to do Tevilas Ezra( and hence erev yom Kippur Tevilah) in the Shower how is it done?
The amount isn't 40 sa'ah, it's only 9 kav. From an IDF Q&A distributed by ShemaYisrael:
Q. How can a soldier who is on duty fulfill the custom of immersion in a mikveh on Erev Yom Kippur?
A. ... The poskim write, however, that one who finds immersion difficult can rely on fulfilling his obligation by pouring 9 kavim of water on himself (depending upon various halachic opinions, that amount can range from between 12.5 to 22 liters of water) in an uninterrupted flow that covers his entire body. This is possible by showering.
That means 9 kav is ~3--6 gallons. Even a low-flow showerhead will use that much water in a 5 minute shower; of course how much of that water wound up on you? Make it a ten-minute shower and I think you're all set. I don't think there's any other special procedure, other than making the shower continuous (not turning it off to get the soap or something).
The "9 kav" requirement allows for water that sat in a storage tank, too (unlike the 40-sa'ah-of-fresh-water for a mikvah). Which means the water can be heated.