If you're using E-junkie to sell the ebook, the most practical way would be to use your E-junkie Transaction Log to determine sales/revenue for that product on a periodic basis (monthly/quarterly/etc.), so you can calculate the share of revenues (or net profits, if you want to deduct selling costs first) to pay to your contributing partner:
http://www.e-junkie.com/ej/help.transaction-log.htm
Every log view includes a summary of the total number of sales, units sold, and revenues for the selected date range and/or product, or you can download the log to a spreadsheet file and do your calculations in there. Note that you must click View Log to apply your custom date/product log search parameters before you can click Download Log to save that custom log view to a file.
If you want your contributing partner to be notified by email every time the ebook sells, you can set up the product to use the Multiple Emails method of our custom/third-party Integration feature:
http://www.e-junkie.com/ej/tips.integration.built-in.htm#emails
You may also wish to set up PDF Stamping to deter file sharing of your ebook:
http://www.e-junkie.com/ej/selling-ebooks.htm
You can combine Multiple Emails notification with PDF Stamping by putting the parameters for both methods together after the o_plug.php in your product's Payment Variable Information URL field, like so:
http://www.e-junkie.com/ecom/oplug.php?&ej_stamp_pdf=true&pdf_allow_copy=y&pdf_allow_print=y&m_emails=user@example.com
