Add the option to assign the sub-process in a portfolio to a system (where the process is automated)

We want to assign a sub-process within a portfolio (mega-process) to a system (Oracle) as the sub-process called ‘Generate PO and send to Supplier’ is done automatically by the Oracle system.
We have Oracle listed on our Promapp systems list, and can use it to assign swimlanes within a process to certain steps, but it does not come up as an option to assign it in the portfolio level.