Hi,
in simple manner - no you can't. Separated file for printing acts like simple pdf - parameters are passed to script, script creates pdf content, and tells your browsers, that this file is pdf. You can't generate content as a file using callback hrefs, because callback hrefs are processed by EPESI content.
But you could create some kind of proxy file - one for whole EPESI, where you will pass parameters to print (as now), and also callback to call. Then your callback will create pdf, and proxy file will serve its content. Like it's done for attachments.
Regards,
Adam