Well, I've just been satisfied in the past to be 'hokey' and hardcode all paths in the crontab entry. It works great!

But you could go other ways. For instance you could add code in your script that assumes the config file is in the same dir as the script you are executing, e.g.:

use File::Basename;
$config = shift @ARGV;
$dir = dirname $0;
chdir $dir;
open F, "<$config" or die "Can't open $config: $!\n";
... parse $config file here ...
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