I would recommend a solar filter but a good ND filter (10 stop) can be used. With that said I did shoot a partial eclipse last October with nothing but a plate glass window for a filter.
The over-sized windows in our office are about a quarter inch think. The glass has some IR and UV filtering properties to help keep cooling costs down. I set my camera to allow the least amount of light in and shot the Sun through the window. The result is that there were three images as the light was refracted through the glass.
(70 mm, ISO 50, 1/8000, f22)
The top image is actual Sun and the two lower ones are the refracted images. What amazed me is that you can actually see some sunspots in the two lower images. I wasn't sure that they really were sunspots until I saw some much better pictures with the spots in the same place and configuration.
I *DID NOT* look through the view finder. Nor did I keep the camera pointed at the Sun for long. I would point the camera in the general direction of the sun and shoot. I would then turn it away and check the results. I ended up with a lot of missed shots but since I was stuck in the office it was neat to actually get a few.
I also showed people how they could observe the eclipse by using a piece of cardboard with a small hole and a sheet of paper.
If you do not have a ten stop ND filter or solar filter I would not suggest using live view. Think of the photo sites on your sensor as ants under a magnifying glass. Even if you turn down the ISO and shutter speed you are still leaving the sunlight blazing directly on your sensor in a nice focused pattern.
