I wish to do something like this:
var showme = false;
$(\'#mydatepicker\').datepicker({
beforeShow: function(input, inst) {
if(!showme) {
Looking through the source, it doesn't look like that is possible currently. You might be able to request that as a feature. If you really want to make it stop (though this is probably a bad idea) you could throw an error in that function. Though this will cause errors to show up for your page and probably is not an option.
Note: I submitted a patch for this and it's now in the released jQuery UI (at least v1.9 and later), although the documentation doesn't mention it. return false in beforeShow will prevent the datepicker from appearing (now).