Hi John,
That’s not currently possible as a standard setting or anything of that order: we’d be open to any feature requests you might post along these lines but I wonder if alternatively you could customize Community Events and its templates to add extra fields, etc, but only expose them if a specific criteria is met (such as a URL query like details=extra), such that the standard form appears when a customer visits:
example.com/events/community/add
And additional fields are exposed when they follow a link to:
example.com/events/community/add?details=extra
A simple test like this would help determine if that parameter is set:
if ( isset( $_GET['details'] ) && 'extra' === $_GET['details'] ) { /* ... */ }
You’d also need to build in a handler to save the extra data, but of course that would be true even if you had a truly separate form. Does that help at all?