Using Saxon, how do I include a compiled stylesheet (sep) in a separate stylesheet (xsl)?

Question

I'm compiling stylesheets (XSL) for use with the SaxonJS into their compiled form (SEP).

$ java -jar saxon9ee.jar -target:JS -xsl:child.xsl -export:child.sef.xml -nogo

I would like to use the compiled child stylesheet in another parent stylesheet via an include.

<xsl:include href="child.sef.xml"/>

But when I compile the parent stylesheet, I get errors.

$ java -jar saxon9ee.jar -target:JS -xsl:parent.xsl -export:parent.sef.xml -nogo
Static error at package on line 2 column 352 of child.sef.xml:
  XTSE0150: The supplied file does not appear to be a stylesheet
Errors were reported during stylesheet compilation

I do not want to have to deliver the child.xsl to the team composing the parent.xsl, only the compiled version, child.sep.xml.