How to concatenate/merge two independent XSLT styleshe

I have two independent XSLT style sheets which work fine when they are executed 
in two steps:

mydoc1.xml-->mysheet1.xsl-->mydoc2.xml-->mysheet2.xsl-->mydoc3.xml

However I would like to avoid the intermediate step (and the creation of mydoc2.xml).
Is there a way to concatenate the two XSLT stylesheets resp. use the output of
the first stylesheet templates as input of second stylesheet templates?

Due to other requirements a piping with the well known pipe symbol (|) on the console
is NOT allowed. The two stylesheets MUST be merged together somehow into ONE physical
stylesheet file.

How can I do this?

Ben