Like this? (Or maybe I don't understand what you want.)

#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1200841

use strict;
use warnings;
use Tk;

my %EntryInput;
my @Entry;


my $mw = new MainWindow -title => 'Simple';

foreach (1..3) {
  $mw->Label(-text => $_)->pack(-side => 'left');
  $Entry[$_] = $mw->Entry(-textvariable => \$EntryInput{$_})->pack(-si
+de => 'left');
  PupupEnterField($mw, $Entry[$_], $_);
}


MainLoop;

sub PupupEnterField{
  my ($mw, $obj, $index) = @_;
  my $menu = $mw->Menu(-tearoff=>0, -menuitems=>[
    [command=>"Read value", -command=>[sub {my $EntryValue=$obj->get; 
+ReadEntryValue($EntryValue, $index)}, $obj,]],
  ]);
  $obj->menu($menu);
  $obj->bind('<3>', ['PostPopupMenu', Ev('X'), Ev('Y'), ]);
  return $obj;
}

sub ReadEntryValue{
  my ($EntryValue, $index) = @_;
  print $EntryValue;
  #print the index of the Entry widget: 1, 2 or 3...
  print $index;
}
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