maybe it does not work with win32 version of perl, but I can read and write from/to stdout/in of another program:

#!/usr/bin/perl
open(BOTH, "|./echo|") or die "error in open: $!";
while(<>){
        print ".";
        print BOTH $_;
        print <BOTH>;
}
close(BOTH) or die "error in close: $!";
[download]

with caller being a oneliner :

print while(<>);
[download]

hope that helps, although it is probably not supported on win32.