How can I load 'utf8' into plperl by default?
The solution I found involes mimicing the utf8 module's AUTOLOAD function in the plperl.on_init setting:

plperl.on_init = 'use utf8; use re; package utf8; require "utf8_heavy.pl";'


This successfully loads and initializes the utf8_heavy.pl file before dropping into Postgres's safe mode for running perl scripts.