Update: I missed the line about "I could arrange that the constructor wraps the subroutine at construction time, rather than de-referencing time". My apologies to the OP. This won't answer the OP's question, but maybe it will be helpful to someone interested in the more general solution "how do I..."

Is your goal to wrap the call to $f in a sub that inserts some before (or maybe before and after behavior)? Or it is to do that and insure that the blessed code ref and $f have the same memory address? And if so, why is this important?

If you don't need the same memory address, you could simply define a constructor that wraps the subroutine in another subroutine, like this:

{
  package Before;
  sub new {
    my ($sClass,$f) = @_;
    my $fBefore= sub { print "Special stuff for class $sClass\n";
                       goto &$f
                     };
    return bless($fBefore,$sClass);
  }
}

{
  package AlsoBefore;
  our @ISA=qw(Before);
}

my $f1=Before->new(sub {print "Hello world!\n"});
my $f2=Before->new(sub {print "Bonjour, le monde!\n"});
my $f3=Before->new(sub {print "Guten tag, die welt!\n"});
my $f4=AlsoBefore->new(sub {print "Boker tov, olam!\n"});

$f1->(); $f2->(); $f3->(); $f4->();
[download]

which prints

Special stuff for class Before
Hello world!
Special stuff for class Before
Bonjour, le monde!
Special stuff for class Before
Guten tag, die welt!
Special stuff for class AlsoBefore
Boker tov, olam!
[download]

Best, beth