XML schema user defined simpletype with case insensitiveness

Just a thought of exploration, I am using a user defined simple type in
my schema
<xsd:simpleType name="VehicleType">
		<xsd:restriction base="xsd:string">
			<xsd:enumeration value="New"/>
			<xsd:enumeration value="Current"/>
			<xsd:enumeration value="Obsolete"/>
		</xsd:restriction>
	</xsd:simpleType>

Here I want "VehicleType" shoould be case insensitive. So "nEw" or "neW"
should be valid.
The work around is I can push all the enumeration but the enumeration
list would be fair long.
SO any suggestion to make a simple type with case insensitiveness,

regards,
-Ranjan