The stories and modelling we are trying but they are yet to have an impact.
I've found stories and modelling really work in the very long term - months at best, probably years. So that is not really meant as an immediate answer to your problem!
Just thought of another one, though. DS 4.5yo has been very receptive over the past year to these two techniques:
1. Ask him to make a triangle using his fingertips.
2. Ask him to breathe deeply as you count the breaths.
In both cases it works best if you're there - sorry - but once they get the hang of it a bit you can shout it from the next room. You have to use a fairly commanding tone. Not scary-commanding, just firm, insistent and authoritative, if you know what I mean. The sort of voice that can get through to somebody in a panic and make them feel like the secure thing to do is exactly what you say.
I think both are basically working because they're meditative techniques aimed at switching off the adrenalin/cortisol.
There was one someone posted here which is very similar. You get them to pretend they are holding a mug of hot cocoa (so it's a circle with fingertips). Then you get them to blow on the cocoa as if to cool it down (so it's measured breathing).
So yeah, just remembered that's what we've done when emotions are running high and seems to get everyone back into a workable frame of mind. That said, I suspect there's going to be a big measure of riding it out... I have to say, excessive clinginess really wears on me quickly, especially when other things need attending to, so best of luck!