I was able to figure out how to do it, even though there seems to be no documentation on this feature throughout the world wide internets. Anyway, here are the steps:
1. Right-click the number box (not from the Fields section, but on the form itself) and select "Text Box Properties"
2. Under the Data tab, find "Data Type" and set it to "Whole Number (integer)"
3. To the right of that, click the "Format..." button: This is the key part!
4. Now you can see at the bottom an option for "use a digit grouping symbol". Right there is how to remove the auto-commas, but initially it is grayed out.
5. Under Format, select the "Number" radio button option. The check box for the grouping symbol is now enabled. Un-check this, click OK.
6. ???
7. Profit!