This is not the cleanest approach, but it's one (untested) way:

package main;

use lib 'plugins';

main();

sub main
{
    load_plugins();
    init_plugins();
}

sub load_plugins
{
    for my $plugin (<plugins/*.pm>)
    {
        (my $package = $plugin) =~ s/\.pm//;
        require $plugin;
    }
}

my @plugins;

sub register_plugin
{
    my ($class, $plugin_subref) = @_
    push @plugins, $plugin_subref;
}

sub init_plugins
{
    $_->() for @plugins;
}

package ExamplePlugin;

sub import
{
    my $caller = caller();
    $caller->register_plugin( \&init );   
}

sub init
{
     # initialization code here
}

1;
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