I can't think of any way to run tasks from parent process and subprocess in parallel except putting a parallel gateway in before entering the subprocess. But it sounds like you'd want the fork of the parallel gateway after entering the subprocess. I don't think you can do that. The only options I can think of are to bring the subprocess elements into the main process so that it's just one process and then introduce the gateway. Or introduce the gateway in the main process and try to move elements from the subprocess and restructure so that the fork of the gateway is where you want it to be.
Or do you mean that the condition for the first exclusive gateway is not being satisified in the way you'd expect?
Do you mean that on first execution you might expect the path to go the lower route into the subprocess and then after going through the script and again through the first task the user does something which should allow the condition to be met to go through the top route? If so I'm not sure what condition it is you have in mind.
Perhaps you could clarify what you mean by 'without any interruption'?