Convert string from param to a nodeset in 2.0

Is there any way in xslt 2.0 to convert a string to a node-set that is
passed in as a parameter?

That is, I would like the calling application to be able to pass in the
string "<foo><bar/></foo>" and then operate on that string as if it were
a node-set.  I want to convert the string inside the stylesheet, not
force the calling application to create the nodeset.

I believe I need to specify type string on the parameter that receives
the string, and then perform another operation on that.  I'm sure I'm
missing something obvious here...

cheers
andrew