A recent post in the OpenWRT forums hilighted the TTL-232R-3V3-AJ USB cable, a TTL Level Serial Converter, or in other words, it takes a 3.3v RS-232 signal and converts it to USB, perfect for use with my WRTSL54GS, thanks to the fact that they also have Mac drivers available. This will allow me to ditch (with some slight regret) my hacked USB serial interface, and simply add a clean looking 3.5mm stereo audio connector to the side of my WRT, which this cable will plug right into.
Several versions of this cable are available for 5v and 3.3v sources, with several alternate ends, the AJ (Audio Jack) version to me seems the most flexible to adding a serial interface as it is easily removable from the unit when not needed.