BEGIN {
  my $ns = __PACKAGE__;
  $ns =~ s/::[^:]*$//;

  eval "require $ns\::Config";
  "$ns\::Config"->import(qw(x y z));
}
[download]

is the same as

BEGIN {
  ( my $ns = __PACKAGE__ ) =~ s/::[^:]*$//;
  my @syms = qw(x y z);
  eval "use $ns\::Config \@syms";
}
[download]

Then add error checking

BEGIN {
  ( my $ns = __PACKAGE__ ) =~ s/::[^:]*$//;
  my @syms = qw(x y z);
  eval "use $ns\::Config \@syms; 1" or die $@;
}
[download]

Since you import, if can also do the job:

sub qualify_ns {
   ( my $ns = __PACKAGE__ ) =~ s/::[^:]*$//;
   return "$ns\::$_[0]";
}

use if 1, qualify_ns('Config') => qw(x y z);
[download]