except with potatoes, the edible crop comes from the roots...
If you were to do that, the stem would produce roots along the buried portion yes, however that takes energy away from other growth and I don't think it would benefit the fruit production, possibly the opposite and you would need to maintain moisture in the structure. Plants know what to do if you let them
roots grow down into soil and feeder roots spread out just under the surface of the soil all around the plant. There's no need to try and change mother natures ideas about tomato roots.
KarenO