Convert text into a png image using GD without using WikiPluginCached. The images are stored in a private <PHPWIKI_DIR>/images/<LANG> subdirectory instead, which are not timestamp checked at all. Delete the .png file(s) if you change anything.
This is a really simple and stupid plugin, which might need some work.
<?plugin text2png text="some text" ?>
See the sourcecode. You'd probably need to adjust $ttfont and text2png_debug.
<?plugin text2png text='Hello WikiWorld!' ?>