I have been in a situation similar to this. Boxed in by Heathrow, Luton and rain (not impossible to fly through, but undesirable with nervous passengers). A 180 was an option, but before resorting to that (and 3nm or so before hitting the rain) I gave Luton a call and they were happy to help. They advised me of a heading to their overhead, without me even asking, which more or less coincided with the VFR lane, so maybe I was luck in that respect. From there I got my self around the rain with no difficulties.
I did give the controller a scare as there was something wrong with my mode C meaning I was indicating an altitude ten times higher than I was flying. Needless to say I was promptly asked to switch that off!
If you are boxed in by clouds and CAS, get onto the people controlling the CAS, you can't talk to clouds!
This didn't seem to stop my pax screaming at them!
