Stefan Esser points out a new patch today - CORE GRASP - from the Core Security Technologies group that provides taint support surrounding the mysql_query function.

Their implementation adds a tainted or not flag for every byte so that it is possible on invocation of mysql_query() to determine any kind of injection.

Unfortunately, Stefan also mentions two big issues it might have from the get-go: the overhead for the memory needed can slow things down and an incorrect parsing in their query handler could lead to injection attacks.