File driver.pl:

use strict;
use TestMeNow;
my %map = TestMeNow::initialize('value', 'Here I am!');
&{$map{'onecase'}{'ex'}}();

File TestMeNow.pm:

use strict;
package TestMeNow;
my(%map, $value, %mapping);
$map{'value'} = \$value;
sub initialize
{
    my(%args) = @_;
    foreach(keys %args)
    {
        ${$map{$_}} = $args{$_};
    }
    my $string = <DATA>;
    %mapping = eval $string;
    return %mapping;
}
1;
__DATA__
'onecase', { 'ex' => sub {print "$value\n";} }