JQM 1.4.0: dynamically set disabled="disabled" to option in selectmenu

JQM 1.4.0: dynamically set disabled="disabled" to option in selectmenu

This attribute disables an option in a selectmenu:
disabled="disabled"

How to set or unset this option in a JQM not-data-native menu dynamically?

This is my fiddle:
http://jsfiddle.net/rCFzP/3/

I tried:
$("#idSel option[value='c']").prop('disabled', true);

This only works when the selectmenu has data-native-menu="true", not when false.
What it does, is adding this property:
disabled=""

Please help! I tried the whole morning to solve this..