I'm sure if you tried hard enough - and were clever enough - you could probably figure out how to eat string beans through your nose, too. But I wouldn't recommend it.
Configure your Apache server with PHP5 ... and leave it at that.
If you absolutely *must* have PHP4 co-located on the same machine, then build it into a *separate* version of Apache, and run it as a separate server (on a separate port, of course).
IMHO .. PSM