This is trivial, except I had to spend a while to re-discover it. So let me post it here.
You generate your JCA stuff from JDeveloper normally.
From OSB console, under project, select "create resource", under "bulk", select "URL or zip".
Remember if you select URL, then OSB can only find the resource from the server that OSB runs on (you may scratch your head for a long time if you are confused).
If you zip, you need to zip yourXYZ.jca and yourXYZ.wsdl.
After it's imported, find the little square and arrow icon towards the right of "JCA Binding", click that to continue.
From Eclipse, the import is similar, right click on your project, select import (except you are most likely on your local file system), so the URL will look like file:///c:/myjca/mytest.jca, remember to select JCA Binding as your type.
After import is complete, then right click on the JCA file, then select "Oracle Service Bus" (down the list, it took me a while to re-discover this :( ), then "Generate Service".