Corion,
This specific case relates more to the next keyword than to last. The idea is that once a particular piece of code has been invoked, it magically disapears.

for ( 1 .. 100 ) {
    next if $_ == 50;
    print "$_\n";
}
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Becomes functionally equivalent to print "$_\n" for 1 .. 49, 51 .. 100;. The meditation isn't about solving for specific cases but having the ability to dynamically change the running code and what would you do with it if it were cheap.

It really isn't like a source filter because you want the code to first be there and then go away while the code is running. I am already pretty sure that there is no way in the existing language to get this optimization without paying more for it then you get out. That's not what the medidation is about though.