Assign Deferred_Call to a variable

I want to call a function from a Deferred_Call in a custom event. No issue with that I hear you say but the function returns a number variable. I want to then store that variable in the custom event and display it back to the user.

So I want to do something like below where My_API.getcount is passed in a value in “attr” and then does a count with that value and returns what it finds

Transaction_SYS.Deferred_Call(job_id_,
                                'My_API.getcount',
                                'PARAMETER',
                                attr_,
                                'Return count');

I want to then assign what it returns to a variable (let’s call it “numvar” )and display that to the user in a warning message box like below.

Client_SYS.Add_Info('PurchaseRequisition', 'WARNREQ: Warning:the number is ' || numvar);

I don’t think this is possible?