After unplugging the injectors I think they just pull out. They'll probably be very tight though.
I would use IPA with 10% Xylene in it. The xylene will attack any really greasy deposits much better (but you'll probably know that).
Injector cleaners are normally 10% xylene/90% parraffin.
I would be worried about the sonic bath cracking the injectors if they have become brittle or something.
Let me know how it goes....I too have sonic baths and access to all sorts of nice smelling solvents !!!