Well I usually activate M-x cperl-toggle-autohelp instead of remembering another carpal-tunnel-inducer ... ;-)

Whenever your cursor is longer than 2 secs over a keyword it'll react. But last that I checked this showed the mini-docs in the bottom-line.

I had to patch cperl-mode to show a yellow tool-tip instead.

update

well monkey-patched with an advice to be more precise ...