Where I've worked with a configuration like this it's always been a "call for release" arrangement with the smaller facilities. For instance, here's a look at KLAX and its neighbors. I've done the narrative on the image from memory, so no promises as to currency or accuracy. I'm sure Westy or someone else can provide better info. In short, LAX tower launches departures off LAX on their own, while Santa Monica (SMO-runway 21) and Hawthorne (HHR-runway 25) must call the departure controller for release on each IFR departure.
When I worked at LA tracon the bane of my existence was a King Air which would launch off HHR every morning around 0630 and need to be worked around exactly the same 737s and MD80s off LAX every single day. This chap would depart VFR before the HHR tower opened and call me for his IFR clearance when he was off the ground, climbing on a 250 heading, wanting to go north. Each day I knew this potential conflict would happen, I knew WHEN it would happen, and I knew exactly HOW it would happen, and still it required more work than anything else I faced all day long! Grrrr.
Dave