Run two apaches on the box, like merlyn said. (Actually, two swarms of apaches, but you get my drift.) Look carefully at your httpd.conf and vhosts.conf; factor out the common chunks, make tiny conf files for the small bits that differ by the two apaches (eg the listen port and perl path stuff), and and use includes on these various files to build up the final production.conf and dev.conf files. Believe me, you don't want to try and keep two sets of conf files in sync -- factor out the commonalities and you'll save time over the long run not having to chase down mysterious conf-related bugs.

UPDATE: Another idea: consider moving dev to its own hardware. (Better, as then bad crashes or slowdowns don't harm production.) The dev machine can be very lightweight usually -- a semi-discarded whitebox a few years old running gentoo could very well be powerful enough for dev work and testing. So what if it can't handle load, or takes an extra second to respond -- its for development. With distinct hardware, you can use exactly the same conf files, directory structures, etc on dev and production, making change management, updates, and rollback much easier.