A simple way you could do it is use onContextMenu to return a JavaScript function:
<input type="button" value="Example" onContextMenu="return RightClickFunction();">
<script>
function RightClickFunction() {
// Enter your code here;
return false;
}
</script>
And by entering return false; you will cancel out the context menu.
if you still want to display the context menu you can just remove the return false; line.