I think you would be surprised at the method I suggested I done it years ago on a Metro of all things.

Use a hard piece of plastic to rub the outside smooth handle of a screw driver works ok.

As for filling use teroson 6700 it's a 2 part adhesive/Filler but tbh I don't think you will need it.

Just ensure you iron is clean as you will leave traces of solder on the plastic.