How do I generate offline transactions in Java? I'd like to develop a Java binding to the Stratum Overlay Network (a server for thin clients). This requires signing on offline transactions.

Can I directly use bitcoinj's API to do this? Can I copy-paste some java from from it?

In shorts, how would I generate/sign offline transactions in Java?
That depends on how the Overlay Network will be handling the transactions. It might follow the standard protocol, or develop its own. In any case, as the ON is still in proposal stage, everything can change still. Best advise is to follow the forum thread and the Google Doc and see where it settles at.