If you ensure the code ref doesn't get freed, all you need is a means of serializing and deserializing the code reference. The following should do the trick (including keeping the code ref alive):

sub submit_request {
    my ($code_ref, ...) = @_;
    my $callback_id = "$code_ref";
    $registered{ $callback_id } ||= [ 0, $code_ref ];
    ++$registered{ $callback_id }[0];
    _submit_request($callback_id, @_);
}
[download]

sub on_response {
    my $callback_id = shift;
    my $code_ref = $registered{ $callback_id }[1]
        or croak(...);
    --$registered{ $callback_id }[0]
        or delete( $registered{ $callback_id } );
    $code_ref->(@_);
}
[download]

Assumptions:

• The response is always handled by the process that issued the request.
• There is only one response per request.