I did end up using threads actually.

In the case that I can't open a non-blocking listener, I make a thread and share the messages in an array. It worked great and I can get the IP from the recv().

Really, the best part is, this is the first time I've every needed to use a thread and now that I know how, it's like there's a whole new world out there.

And for posterity, here is my original non-blocking loop along with my new magical threaded version.

sub listen {
    my $this = shift;

    if( $this->{blocking} ) {
        if( not $this->{blocking_thread} ) {
            $this->{blocking_thread} = new threads( \&_blocking_listen
+, $this );
        }
        
        my @msgs = map([ split /^G^G/, $_ ], @global_shared_messages);
        @global_shared_messages = ();

        return @msgs;
    }
    
    my @msgs = ();
    my $msg  = "";
    while( my $portaddr = recv($this->{in}, $msg, 1024*1024, 0) ) {
        my ($portno, $ipaddr) = sockaddr_in($portaddr);
        my $ip = inet_ntoa($ipaddr);

        push @msgs, [$ip, $this->_transform($msg)];
    }
    
    return @msgs;
}

sub _blocking_listen {
    my $this = shift; {

        my $msg  = "";
        while( my $portaddr = recv($this->{in}, $msg, 1024*1024, 0) ) 
+{
            my ($portno, $ipaddr) = sockaddr_in($portaddr);
            my $ip = inet_ntoa($ipaddr);

            push @global_shared_messages, "$ip^G^G" . $this->_transfor
+m($msg);
        }
        
        redo;  # we stay in here forever, btw.
    }
}
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