This reminds me of the old javascript way of running xsl.
In order to set parameters, you would actually have to change the values of the parameters of the elements in DOM of the xsl, then run the transformation.
Anyways, I think you can use SelectNodes("//xsl:template[@match]/xsl:param/@name", nsmgr)
where nsmgr is your namespace manager, and has the namespace xsl defined.
Assumptions:
You have a main template which uses match.
When you call your other matched templates, you don't use parameters; (Usually the case.)