$dynamic_configuration = 'CONF-A';
use $dynamic_configuration;

##</code><code>##

if ($A) {
  use CONF-A;
} elsif ($B) {
  use CONF-B;
} elsif ($C) {
  use CONF-C;
}

##</code><code>##

%conf = (CONF-A => 'foo', etc...,
         CONF-B => 'bar', etc...,
         CONF-C => 'baz', etc...);

##</code><code>##

$x = 'A';
eval "require CONF-$x";
import ????? qw(var1 var2...);