I see that this gets posted every now and then and a CC comes along and rescues the question - I wasn't sure how long to wait to see if it would be seen/rescued on its own so I figured I'd just post anyway:
https://community.atlassian.com/t5/Marketplace-Apps-questions/Script-Runner-Adding-lozenge-to-HTML-scripted-field-to-show/qaq-p/1021427
