Thanks for the help above and I've done it like this,

package PARAMIN;
use strict;
use Tk;

our (@ISA, @EXPORT, @EXPORT_OK, %EXPORT_TAGS, $VERSION);
require Exporter;
$VERSION = 1.00;


@ISA = qw(Exporter);

@EXPORT = qw(inputWindow);             
@EXPORT_OK = qw();

sub inputWindow{
my $result = $_[0];
my $prompt = $_[1];


my $mw = MainWindow->new(-title=>"Parameter Input");

my $label = $mw->Label(-text=>$prompt)->pack();
my $in = $mw->Entry(-textvariable=>$result, -width=>30)->pack();
$in->bind('<Return>', sub{$mw->destroy} );

$in->focus;
MainLoop;
}

1;

package RESULT;
sub TIESCALAR{

    my $class = shift;
    my $state;#= 0;
    #print "IN TIE\n";
    return bless \$state, $class;

}
sub FETCH{
    my $self = shift;
    
    return $$self; 
}

sub STORE{
    my $self = shift;
    $$self = shift;
    #print "IN STORE\n";
}
1;
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Called in the same way as the original post.

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