No, I didn't try beforehand. But just a minute ago I gave a try, but alas, an error. To be sure I checked options[contourplot] and exclusions is part of the options there. Somehow I do something wrong, but it should be possible.
Hi Chiel
Instead of Exclusions, have you tried using RegionFunction? e.g.
Exclusions
RegionFunction
RegionFunction -> (#1 + #2 != 0 &)
