Or with less punctuation:

use strict;
use warnings;

use IO::File;

my $stuff = 0.4312342134234234;
my $morestuff = 0.2432134234342342;

my $fh = IO::File->new('io_heredoc_prob.out', 'w') or die $!;
printf $fh <<'__EOFOO__', $stuff, $morestuff;
Some stuff: %.4f
Some more stuff %.4f
__EOFOO__
[download]

Output:

$ cat io_heredoc_prob.out
Some stuff: 0.4312
Some more stuff 0.2432
[download]