@Gary_Willmott - after taking a look at your App and experimenting with it a bit, I think the solution here is to essentially create a form within a form.
I’ve sent you a video privately that explains in detail, but essentially the idea is that if a User wants to add a new Surfer, we allow them to do it from within the main form. The new surfer will then appear in the multi-select and can be included when the form is submitted.
This is something that can only be done with a custom form.