Remove AU2 Hood/Bonnet Front Lip/Trim with Rusty Nuts

[asimplelife]

I can't find a thread already for this? Maybe the info is buried in a more general thread somewhere?

Its for a high series bonnet.
And I've got 2 with the same problem.
The Lip/Trim is plastic.
There are 5x 10mm nuts under the front edge of the bonnet.
Then there is a double headed screw/bolt, which screws into the plastic Lip/Trim, then bolts through the bonnet to the nut.
Obviously moisture gets into the bolt/not and they seize.
The screw then undoes from the plastic Lip/Trim.
Leaving the double headed screw/bolt attached to the nut and stuck in the bonnet.

I've tried vice grips to clamp the screw head.
But I can't get enough purchase to break the thread.
Have tried WD40 with no improvement.

Before I give up and grind them out, are there any obvious solutions I am missing?
Thankyou.