Filter by array parameter

I need to know how is possible to pass an array string to a Xpath expression
to filter the results.

For example :

<xsl:param name="supplier_param" select="Alitalia,ryanair"


<xsl:for-each  select="msxsl:node-set($base)/item[(supplier =
$supplier_param or not($supplier_param)) ">

In this case I must pass as parameter the value Alitalia,ryanair to get the
results for this  suppliers.

But in this way I get no result.

It' possible in xslt 1.0 pass a an Array as in SQL : WHERE IN
("value1,value2") ?

Thanks in advance.