Multiple masters / custom letters

I’m working with multiple masters and I have some characters that need to be “customized” in the heavier weights. (Oslash for example) What’s the best way to handle that situation? Can individual characters be exempt from the interpolation?

This works: https://www.glyphsapp.com/tutorials/alternating-glyph-shapes-with-multiple-axes

The bracket trick should work, too.

Excellent. Thanks everyone.