Inject keyboard event to textarea

On HTML page I want to keep TEXTAREA controls read-only until the user starts typing characters. All other keyboard events should not change the read-only status. In my script, on the first typed character event the handler makes the control not read-only, but that character does not go to the control itself.
I tried to do the following:

$(".textarea").keyup( function(ev) {
    var k = ev.keyCode;
    var inp = ev.target;
    if(  inp.readOnly && k >= 42 && k <= 90 ) {  // an alphanumeric
    	inp.readOnly = false;
        inp.select();  // without this IE do not accept typed in characters at all
        // i tried this:
    	var sev = $.Event("keypress", {keyCode: k, which: k});
        // and that:
    	var sev = $.Event("keypress", ev);
    	$(inp).trigger(sev);
    }
} );

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Whatever I tried, the first typed character is lost, the second goes to the control.