How does one show the difference between dependant and independant nasalisation using the IPA?

I'm transcribing breton words and wondering how to show the difference between e.g. 'da~nvad', with historical nasalisation [v<m] and 'ka~na' - simply co-articulation. There is often a significant and audible difference in the quality of this nasatisation which I cannot show with a simple tilde.

Guto