I don't know anything about your system but probably wouldn't advise hacking the perl script itself. Instead, I'd create a shell script for cron to run using the shell script's absolute pathname.

In that script I'd set up whatever environment variables that cron either doesn't know about or uses some default value that isn't what you want - man 5 crontab should provide that information. One of those environment variables might be PERL5LIB which modifies @INC - see perlrun - ENVIRONMENT.

The shell script would then run the perl script using the absolute pathname of the perl you want to use. You might want to use command switches such as -Idirectory which modifies @INC - see perlrun - Command Switches.