Yip just parse your user input and check for ||, replacing with some other odd string where necessary. Something really odd.
$str = str_replace("||", "%liberaceplaystennisontuesdays%", $str);
Then when you pull the data backout of the flatfile, reverse it:
$str = str_replace("%liberaceplaystennisontuesdays%", "||", $str);
The odds of someone typing something like "%liberaceplaystennisontuesdays%" are pretty slim I reckon.
By the way, you're ISP sucks... 🙂
adam