Stripped brake line flare nut...damn it !!!

[Porsche Pete]

So the boxster is up on the axle stands today...wheels off and had a good wash under the arches while there..

Ahh will do the Stainless Goodridge lines first i thought...then pads and rotors
and then get my shiny new wheels on .................

9mm and 11mm Flare nut wrenches in hand and a good dose of WD40 lube...
two lines went fine..no problem but despite using proper wrench have managed to strip the flange off one of the nuts
Have tried some vice grips but still not budging!! at the moment
Have called it a day...miffed...gave another good shot of penetrating lube and will attack again in the morning...

Any ideas on shifting this nut?? cleaned the lines down too before starting, and clean enough to eat yr dinner on under there...only done 40k
Thinking heating it up ??

GOOD TIP OF THE DAY;
Give under your wheel arches a good coat of silicone ( i use stuff for car tyre walls, i buy it in 5ltr cans from valet suppliers) be careful and make sure you cover up yr rotors.. Brings the black wheel arch liners up a treat and repels dirt and water like a treat.....
Now those bloody brake pipes.....Grrrrrrr