Good thing memory grows on trees these days ...

use strict;
open(FH, "really_big_file") or die("doh - $!");
my $filestr = do { local $/; <FH> };
$filestr =~ s/(.{150})/$1\n/gs;
[download]

This puts the whole file in $filestr, then sticks a \n after every 150 characters. After that you'll probably want to put $filestr somewhere (probably not the original file in case you trample the data :-)
HTH

broquaint

Update: Ok, per trs80's node I should warn you that this is not a great solution as it will undoubtedly be quite slow and take up large amounts of memory (i.e > than the 25MB file size). But if you've got time and hardware on your hands, TMTOWTDI.