I had the same problem and I my solution was this:
HTML:
<form id="processForm.php" action="post">
<div class="input check_boxes required wish_payment_type">
<div class="wish_payment_type">
<span class="checkbox payment-radio">
<label for="wish_payment_type_1">
<input class="check_boxes required" id="wish_payment_type_1" name="wish[payment_type][]" type="checkbox" value="1">Foo
</label>
</span>
<span class="checkbox payment-radio">
<label for="wish_payment_type_2">
<input class="check_boxes required" id="wish_payment_type_2" name="wish[payment_type][]" type="checkbox" value="2">Bar
</label>
</span>
<span class="checkbox payment-radio">
<label for="wish_payment_type_3">
<input class="check_boxes required" id="wish_payment_type_3" name="wish[payment_type][]" type="checkbox" value="3">Buzz
</label>
<input id='submit' type="submit" value="Submit">
</div>
</form>
JS:
var verifyPaymentType = function () {
var checkboxes = $('.wish_payment_type .checkbox');
var inputs = checkboxes.find('input');
var first = inputs.first()[0];
inputs.on('change', function () {
this.setCustomValidity('');
});
first.setCustomValidity(checkboxes.find('input:checked').length === 0 ? 'Choose one' : '');
}
$('#submit').click(verifyPaymentType);