If I read you right......
If you can get some,"Plus Gas" releasing fluid and then wrap a rag around the bobbin and use mole-grips after heat ?
Also when trying to remove seized bolts etc always tighten slightly first to try and crack the corrosion seal.
Another great homemade release fluid is a 50/50 mix of Acetone and ATF but I've also used Acetone and old Brake fluid,
https://www.youtube.com/watch?v=CESDxCloCoQ
Asda do an Acetone nail varnish remover that can be used for this and other little jobs on the bike like cleaning areas as Acetone is not has destructive as paint thinners and evaporates quickly.
To prevent this problem for myself I used copper-slip/copper grease on my Rear paddock stand bobbins when I fitted them
