<form ...> <input type="submit" accesskey="S" value="Submit"/> </form>
would submit the form by typing Alt+Shift+S.
Not exactly Ctrl+Enter, but something people can learn.
We can also set up that accesskey thing, seems neato.
Progressive enhancement is a forgotten art I was initiated to a more than a decade ago.
I would argue that with simple explanatory divs one could enhance the quality of life without invoking Balrogs that potentially threat the users security.
scripttag, without triggering further request to load further js or json.
It's not just a matter of security: the overall rendering will be faster and the experience better.