Can I pass in a different sys_siteid into $rx.asmhelper.assemble?

I have a rather odd situation. We have two sites built site by side in our Percussion instance, but site B publishes as a subsite of site A (in a subdirectory). Site B was developed by another contractor at the same time Site A was being built. But now the client wants the same top nav and masthead applied to both Site A and Site B.

The top nav in site A is built using this slot
#slot(“rffNav” “” “” “” “” “template=ntpSnNavTop”)

Can I use the same slot in site be and assemble it and pass in the Site A site ID? (say Site A has site ID = 306)

Can I write something like…

to get Site B to publish the top nav of site A?

Or is there another way to do this?