Is there an easy way to access custom fields from an Issue Panel?

I’ve installed and run the sample app which adds a custom field to Jira and lets you easily access it from the field pane on the right side of the screen.

I’m wondering if there is a simple way to read and write custom fields in an Issue Panel - or must that be done via an API? For example, if I could access a custom fields context from within an Issue Panel, I could use the functions defined in the custom field module.