sorting strings question

I have a concrete example:

When I have following strings ['BSS84/A2', 'BSS84/DG', 'BSS84'],

default sorting results in:

BSS84/A2 -> BSS84/DG -> BSS84

But the customer wants them sorted like

BSS84 -> BSS84/A2 -> BSS84/DG


What's the easiest way to accomplish this?
Do I need to write a custom comparator function or can I use some <xsl:sort>
shortcuts or is the only way to use collations?

Thx in advance,
Robby Pelssers