Setting the DEFAULT BUTTON attribute to -1 is supposed to disable Enter/Return:
DIALOG “QUESTION”,P$(1),Btn;SET (“DEFAULT BUTTON”:-1)
However, this did not work for me. I tried setting it to 1, which did work to make “No” the default button. So, I assume -1 not working must be a bug. I will get this submitted and we should be able to fix it.
If you want to discuss this further, you can reach me at firstname.lastname@example.org