You could override the binding yourself, for example

$dialogBox->bind('<Return>' => undef);
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that would force the user to click a button.

Additionally, you can play with the binding when shifting focus on tabs, like

$dialogBox->bind('<Tab>' => sub{  
             #get currently focused button
             $dialogBox->configure(-focus => $my_focussed_button);
              # there is also forceFocus which may help force it
              });
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As a last resort, you can always make your own dialog out of a toplevel window, and setup the bindings to behave anyways you want.