I'd strongly encourage you to not install to your customers machines directly from CPAN. You want the opportunity to be the first to know when one of those CPAN modules (or how you use it) breaks, not leave it to your customers.

And installing specific versions of distributions from CPAN is out because you never know when authors will clean up their directories.

Which leaves you doing your own distribution and installation of known good versions. But then you have the headache of possibly dealing with the customer using perl for other things and with their own module version requirements.

Put all that together, and the ideal solution starts to look very much like PAR.