Why do you think require won't work? The only catch is the "1;" needed at the end of the required file.

--- File: a.pl ---
use DBI;
use MIME::Base64;

BEGIN { require 'b.pl'; }

$VARA = 'a';

local $\ = "\n";

testb();                      # Never imported.

sub testa {
   print("and we're back");
   print($VARB);              # Never imported.
   print(catfile('1', '0'));  # Never imported in this file.
}

--- File: b.pl ---
use File::Spec::Functions;

$VARB = 'b';

sub testb {
   print("magical newlines");           # $\ taking effect.
   print($DBI::VERSION);                # Never used DBI in this file.
   print(encode_base64("Hello World")); # Never imported in this file.
   print($VARA);                        # Never imported.
   testa();                             # Never imported.
}

1;

--- output ---
magical newlines
1.28
SGVsbG8gV29ybGQ=

a
and we're back
b
1/0
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