Solution 1:
Put the explicit path to your Perl interpretator as the magic line, eg: Of course, you have to run the script that modifies your PATH prior to the script execution.
A script example:

#!/app/perl/5.8.1/bin/perl
printf "Hello, World!\n";
[download]

The drawback is that you have to update gazillions of magic lines when we change to a new Perl version.

Solution 2:
Use a symbolic link to point to your current Perl version. Still you have to run the script that modifies your PATH prior to the script execution.
A link example:

ln -s /app/perl/5.8.1/bin/perl /home/foobar/current_perl

A script example:
#!/home/foobar/current_perl
printf "Hello, World!\n";
[download]

The (smaller) drawback is that you have to edit the magic line if you deliberately want to override the Perl version.

Solution 3:
Use a wrapper that selects a Perl from the path. Still you have to run the script that modifies your PATH prior to the script execution.
A script example:

#!/usr/bin/env perl
printf "Hello, World!\n";
[download]

If you don't like the selected Perl you can re-modify your PATH an continue.

Additions requirements: When investigating this I found that you sometimes want to save your scripts in a CM-system, eg. ClearCase. Furthermore you want to execute old verions of a script with that old Perl version that existed when it was developed.

Solution 4: (A combination of 2 and 3)
First you have a symbolic link in your CM-system that points to your selected Perl version. This link is baselines along with the script source.
A link example:

ln -s /app/perl/5.8.1/bin/perl /vobs/foobar/current_perl
[download]

Secondly, you have a better wrapper that you put in the magic line:
A script example:

#!/vobs/foobar/perlwrapper
printf "Hello, World!\n";
[download]

The wrapper does ths following: 1) Checks if the environment (PATH etc.) is compatible with the Perl that is pointed to by the symbolic link.
2) If not, the environment is adjusted, using the script mentioned above.
3) Starts Perl with the proper arguments.