The Activity Starter method would be something like this (again, not tested):
Which means we cannot automate a call.
1) Set the number to call in the Clipboard and pop-up a Notifier to tell the User to paste it into the dialer TextBox;
2) Ask Google directly to give your App Permission to call direct - with a valid reason for doing so. I don't know of anyone who has successfully argued their case with Google;
3) Use an alternative App distributor instead of Google Play (e.g. Amazon). That's a loop hole which I would expect Google to clamp-down on in Android, if they haven't already done so.