I had a similar experience with Storable. Is there a big problem with simply cloning bar: %$ref = %$bar? Alternatively, what about making $ref into a proxy for $bar:

{
    package Proxy;
    our $AUTOLOAD;
    sub AUTOLOAD
    {
       my $self = shift;
       my $name = $AUTOLOAD;
       $name =~ s/.*://;
       return if $name eq 'DESTROY';
       $self->{bar}->$name(@_);
    }

    sub isa { (shift)->{bar}->isa(@_) }
    sub can { (shift)->{bar}->can(@_) }
}

sub some_sub {
    my $ref = shift;
    %$ref = (bar => $bar);
    bless $ref, "Proxy";
}
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This code is untested, but I've had success with similar techniques. It assumes that $ref is a hash reference-type object, and that you never access the contents of the hash directly.