Effectively i had no success in append mode (all tests on windows as above) as suggested by Anonymous.

The possibility to open an handle to a string is in the Perl Faq and also the possibility to dup a filehandle is in the Perl Faq. Also, as you already said, is worth to read open and search for the phrase "Perl scalars".

The crucial point seems to be spotted by Anonymous here above: the '>&' or '>&=' trick works only with descriptors and in your case ELISHEVA we have no descriptor:

# perl -e ' open $h,">", \$s or die; print qq(fileno: [).fileno ($h).q
+q(]\n);'
fileno: [-1]
[download]

And fileno doc says it explicitly:

Returns the file descriptor for a filehandle, or undefined if the filehandle is not open. If there is no real file descriptor at the OS level, as can happen with filehandles connected to memory objects via open with a reference for the third argument, -1 is returned.

So it seems only an hedge case worth to be inserted in the open documentation and in the relevant Faq

As side note i remember the $^F or maximum file descriptor. How an handle opened on a reference acts in respect of this? is close_on_exec set in the right way? or this will result in zombie handles?
Might be worth to clarify also this in the docs.

L*