I think Microsoft Biztalk is still using XSLT 1.0 so there's likely to be very little support for alternative collations, unless Microsoft have done something specific to their product. If you're only dealing with letters and digits, then a simple solution is to set up a translation table something like this:
Code:
<xsl:sort select="translate(xxxx, 'ABCDEF...Z0123456789', '0123456789ABCDEF...Z')"/>
You can obviously extend this to cover as many characters as you want. The first list should contain the characters in Unicode order, the second list in the order that you want them to collate (I think I've got that right...)