Since use module is the same as 
BEGIN { require module }

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, you could do something like:
BEGIN {
  my $version = (($0 =~ /2(?:\.pl)?$/) ? '2' : '');
  require "LayerB${version}.pm";
}

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If you are using the form use module LIST you'll need to call import:
BEGIN {
   # set $version based on $0
  require "LayerB${version}.pm";
  "LayerB${version}"->import(qw(A B C));
}

[download]

update: added import part, cleaned up $version setting

In reply to Re: Conditional use of 'use' by bikeNomad
in thread Conditional use of 'use' by dvergin

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