Perhaps you could just skip out the second step and implement something like swrite() as demonstrated in perlform e.g

sub swrite {
  local $^A;
  formline( $_[0], @_[ 1 .. $#_ ] );
  return $^A;
}

my $output = swrite(<<FORM, 1 .. 5 );
@<<<@|||@>>>@|||@<<<
FORM

print "format: $output", 

__output__

format: 1    2     3 4  5
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