Orbeon multi rest feature

Hi,

Is there possibility do reach following effect in Orbeon PE using service and actions (or maybe other) controls:

I have many http services, which response body looks like:

<user>
   <number>n</number>
</user>

I don't know how many services I have when I creating form in formBuilder. It may be 1-99. Information about number of services and their urls is knowing only when user is filling this form. Suppose that we have n services with urls: http://service_n where 'n' is order number. And now, I want to sum <number> from provided services. Is it possible to reach that using controls in PE version?

regards,
Tom