1) Create Java Eclipse Plugin project
2) Convert to Groovy project
3) add org.codehaus.groovy to Require-Bundle or add
Import-Package: groovy.lang,
org.codehaus.groovy.reflection,
org.codehaus.groovy.runtime,
org.codehaus.groovy.runtime.callsite
This is all. At least for an extremely simple example this works great. I haven't tested anything complicated yet.