First you don't need use Crypt::SSLeay; -- LWP will do all job for you.

Nope, that's not true. LWP delegates the handling of setting up the SSL connection to Crypt::SSLeay, or, more specifically, the Net::SSL package therein (which LWP will load on demand). These days, Crypt::SSLeay itself is an empty shell.

On the possibility that I could be misunderstanding you, let me put it another way: yes, the declaration is not needed in the client code, but the Crypt-SSLeay distribution must be installed for an https connection to work.

While you may not like the environment variable hack, it's about the only way to transmit out-of-band information to a delegated-to package, without polluting the call stack all the way down. I suppose some sort of API could be added at the class level, but it would probably be tricky to get right when threads are taken into account.