Programmatically skip an NUnit test

Is there a way for an NUnit test to end and tell the test runner that it should be considered skipped/ignored, rather than succeeded or failed?

My motivation for this is that I have a few tests that don't apply in certain circumstances, but this can't be determined until the test (or maybe the fixture) starts running.

Obviously in these circumstances I could just return from the test and allow it to succeed, but (a) this seems wrong and (b) I'd like to know that tests have been skipped.

I am aware of the [Ignore] attribute, but this is compiled-in. I'm looking for a run-time, programmatic equivalent. Something like:

if (testNotApplicable)
    throw new NUnit.Framework.IgnoreTest("Not applicable");

Or is programmatically skipping a test just wrong? If so, what should I be doing?