I would have no problem trying this. Seems like a good idea. I'm currently growing in a box with rotted manure as the base and I'm planning on putting even longer rotted manure on top to get more potatoes.
Part of the problem with adding earth to the potatoes is that it depends on your soil type. I couldn't do your technique since my soil is too heavy clay. Hence the manure and
compost trials.
If you have soft, crumbly soil I would go for it. If not you could mix it with compost or manure to get something more hospitable to new potatoes.
The other problem is getting enough soil, but it looks like you'll be digging anyway, so there you go.
William