From Debian user Josh Triplett:

I configure my system such that I have full sudo permissions, so in
particular I have permission to use "sudo -E" to preserve the entire
environment.  I like the idea of filtering the environment via a
whitelist, to avoid potentially undesirable behavior when running
programs as another user; however, I'd like the ability to extend this
whitelist without resorting to the big hammer of -E.  Thus, I'd really
like a command-line option or (more importantly) an environment
variable which would specify additional environment variables to keep,
treating them as though specified in /etc/sudoers with env_keep.  I
could then set that in my .bashrc to preserve some useful environment
variables, such as LESSHISTFILE (so I stop getting a root-owned
~/.lesshst in $HOME), LESS, EDITOR, EMAIL, PROMPT_COMMAND, GREP_COLOR,
and GREP_OPTIONS.