You need to create a closure instead: 
$md_config->{"[cust_num]"} = sub { $web_services->GetCustomerNumber(@_
+) };

[download]
That puts one extra subroutine call on the stack though. If you have anything that is stack-sensitive (calls caller, for example), you'll need to use a goto to get rid of that extra hop: 
$md_config->{"[cust_num]"} = do {
  my $meth = $web_services->can("GetCustomerNumber");
  sub { unshift @_, $web_services; goto &$meth; }
};

[download]

-- Randal L. Schwartz, Perl hacker

In reply to Re: Storing/Calling References to Instance Methods by merlyn
in thread Storing/Calling References to Instance Methods by mlong

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