Adding circuits to the existing fuseboxes?

[donkmeister]

Has anyone added any circuits to the blank slots/ways in any of the LS460 fuseboxes? 

I have done this on other cars in the past to avoid using fuse-taps, but for the LS460 the fused power goes out through multiway connectors and I've not been able to find info on which slots are connected to which pins (nor what pins I'd need to buy to populate the blank parts of the connectors). I'd rather avoid having to buy a set of used fuseboxes on eBay to test!

Specifically I'm interested in the boot fusebox and either of the passenger compartment ones. It's not to add anything particularly exciting (towbar wiring and a dashcam) but it saves having to piggyback off something else or having to leave the fusebox cover off for a fuse-tap.