Narrow buffer to the results of an isearch?

[Ryan Newton]

Maybe this is impossible, I certainly haven't found anything on it yet.

What I want is to mask the current buffer to all lines matching an  
search.  Unfortunately I don't know if narrow-to-region can be used  
for this, because the region is defined as a continuous area of text  
between the mark and the point.

Has anyone hacked up support for discontinuous regions?  Or some  
other way that I can filter the buffer to only my lines of interest?

--Ryan