I would not include LAX (SoCal approach) in the list of those that might deny. In my experience, SoCal has been most accomodating.
Heck, last time through I was headed over the top southbound to San Diego. We were receiving flight following. A bit north of LAX the controller asked for my plan through the LAX Class B airspace. I 'fessed up "I'm not familiar so we're going around the east end" (I calculated the route would only add about 5 minutes to the flight). Then added "But if you have a better idea, I'm all ears".
"Stand by, I'm working on it" was his reply.
A minute later he asked "Can you navigate direct VNY (Van Nuys), direct SLI (Seal Beach)?" The simplicity of the question, akin to "can you walk erect without aids?" too me back a second. I replied with a hearty "Yes Sir!"
"Ok, the next controller is going to clear you for the xxxx transition. Just smile and nod, it's what I just gave you".
(And she did... worked out like a charm. The transition put is straight over the heart of LA).
Every TRACON should be as accomodating!