Create a button hotspot on the form. On a separate line above it , put "<!--" and add a line below it with "//-->" using the HTML paragraph style. This will comment out the Domino button on the browser.
Another way to get rid of the Domino Submit button is to create a hotspot button on the form but do not assign a name or any code to it. It will not appear when you compose the document from a browser.
And for your amusement and all the other variations on this, check out the How To Hide A Submit Button web site :-)