Hi Stefan,
Here's a few ideas then.
Sorry, all of the ideas were based on the MPC8349EA, which I am currently using. I did not look at the ppc460 documents, as I was just putting ideas 'out there'.
When the MPC8349EA is booted, you can enable the peripherals while leaving the core in reset. The IMMRs are memory mapped to PCI via a 1MB BAR, and there are several other BARs setup to have 1MB windows. The IMMR registers can be accessed to setup the memory map of the target processor, and setup the inbound translation windows. I've been using this technique to check out all of my hardware, and DMA over PCI, DDR, and local buses.
Given that you don't think any of my suggestions are possible, I'll have to go download the ppc460 reference manual and convince myself :)
Ame, feel free to chime in if you think any of the ideas are possible.
Cheers, Dave