An old Larousse offers moyen ingénieux, parfois peu scrupuleux for combine and I don't think the peu scrupuleux applies here - there's no sense of deception in the song.

So "I have my system" in the OP is near the mark, though 'system' has come to mean something mechanical rather than human. 'I have my scheme' perhaps, but to me that sounds unpleasant.

'Trick' is a tricky word. In this case it's 'trick' as in 'the trick is to ignore them' rather than in 'I play a trick on them'. 'I have my trick' doesn't work. 'I have this trick' is better.

I am reminded if the '60s film 'The Knack - and how to get it'. Knack means almost the same - 'the knack is to ignore them' - but it's more positive and sounds right to me for a '30s popular song. So my suggestion for a title is 'I have this knack'.