That's a shame, since you can get the right results with XS function aliases:

#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"

#include "ppport.h"

#define SI_NOT  0x01
#define SI_REV  0x02


MODULE = String::Index          PACKAGE = String::Index


int
cindex(SV *str, SV *cc, ...)
PROTOTYPE: $$;$
ALIAS:
  ncindex = 1
  crindex = 2
  ncrindex = 3
CODE:
{
  /* you use the 'ix' variable in here to
     determine which alias of the function
     was called.  ix = 0 means 'cindex',
     1 means ncindex, and so on */
}
[download]

I suppose then you could get a similar effect in Perl like so:

sub sub_alias (\&;$) {
  my ($func, $ix) = (@_, 0);
  sub { $func->($ix, @_) };  # that's sub { ... }'s @_, not sub_alias'
+s @_
}

*foo = sub_alias &bar, 1;
*blat = sub_alias &bar, 2;
*gunk = sub_alias &bar, 3;
[download]

The only catch here is that when you call bar(), there won't be that extra argument at the beginning. You can be sneaky, therefore, and do something like this:

sub SubAliasIndex::new { my ($class, $ix) = @_; bless \$ix, $class; }
sub SubAliasIndex::ix { ${ $_[0] } }

sub sub_alias (\&;$) {
  my ($func, $ix) = (@_, 0);
  sub { $func->(SubAliasIndex->new($ix), @_) };
}

sub bar {
  my $ix = (@_ and UNIVERSAL::isa($_[0], 'SubAliasIndex')) ? shift->ix
+ : 0;
  # ...
}

*foo = sub_alias &bar, 1;
*blat = sub_alias &bar, 2;
*gunk = sub_alias &bar, 3;
[download]

It feels like overkill to me. ;)