You can grow tomatoes upside down. Theoretically the bag idea would work but my concern is how to hang the bag so it doesn't fall. In time plastic will get brittle and tear too. It could also tend to tear open enlarging the planting hole as the weight of the soil and water bears down on it.
The following web site has an article on growing tomatoes upside down in a container or bucket. It should be helpful to you:
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