Options can be passed via JavaScript or data attributes:
$('.selectpicker').selectpicker({
dropupAuto: false
});
or
<select class="selectpicker" data-dropup-auto="false">
<option>Mustard</option>
<option>Ketchup</option>
<option>Relish</option>
</select>
You can also set this globally:
$.fn.selectpicker.Constructor.DEFAULTS.dropupAuto = false;