I've seen this before.. apart from getting your PHP app developers to check their code, and making sure you have up-to-date versions (from your distribution) of PHP and apache, there isn't much you can do.
If you're running an Op-Code cacher (eaccelerator, APC or XCache), you could try turning them off, they're known to cause the odd segfault.
In the past, we've had to deploy some impressively hackish solutions to a segfaulting system, for short-term fixes, of course.