I can't comment on the corn starch. It should be fine. Try putting some in the corner of your bin and see how it goes.

As for the flour, it will make a mess if you put in a lot at once. The flour will get moldy before the worms get to it. The mold will form a tough ball that the worms cannot get into. Once the mold has done its thing, the flour will absorb water and get mushy. At that point the worms will have a feast. But it may be a couple of weeks before that happens. (I'm basing this on my experience with bread and rice, both cooked and raw.)

Grains tend to get hot in the bin too. I don't know whether that would happen with flour. If you really want to feed flour to the worms, you might want to sprinkle small amounts into the bin every week or so. Or try a small amount in one corner and see what it does.

Corn meal, ground as coarse grit, will have texture; fine meal & grit you can dust on. Like other grain it is more carbon than nitrogen; carbon is found cheaper in scrap cardboard/paper & the worms adore their texture.
Corn starch is a food industry thickener that the worm bin's water content will make into goo, unless dusted sparingly. A high temperature stage must be achieved before corn starch dissolves fluidly.
Baker's flour, unlike corn meal, has gluten which means a higher nitrogen component; gluten will give you isolated gooey spots, unless dusted on sparingly. The nitrogen benefit derived from any grain's protein could be more inexpensively supplied.
If you are desirous of primarily castings production then plan on giving the worms more of the carbon & proportionately less of wet nitrogenous feed stock. Remember to monitor their bin for excessive heat generation if you really load in nitrogen or fresh green matter.

Thank you sbryce and gringojay for your reply. I have both sitting in my cupboard for a long time and was going to throw them out. Then I thought of feeding them to the worms, since they like the starch in cardboard so much. Ok, I'll be careful and sprinkle just a little bit in a corner and see how it goes.
Or better still, I might cook some in a bowl in the microwave, freeze it in an ice-cube tray(probably just 1/2 the hight)and drop one cube with every feeding and store the rest in Ziploc. Might be easier to monitor and easier to remove if need be. Thanks for the inspiration. Who knows, maybe that will produce real fat worms. Jay!
Otis

I added some corn starch to invite some worms in the soil where my Plumeria is growing. But on reading more about it I realized that it's different from cornmeal. Will it still have the desired effect in encouraging worms?