If *I* had time to design all this stuff........... (which I don't).
I would start by designing a sniffer that worked at 10.4 kbps VPW so I could watch the bus.
I would also design that sniffer so that it automatically switched over to 41.6 kbps VPW when required.
I would use that sniffer on something like a Hypertech Power Programmer.
I would pull the flash chip on the HPP and read the file. It's easier to work with than a PCM chip.
I would use my sniffer to watch commands that are being sent/received, and I'd also figure out what those commands caused the CPU to do in the PCM. Store some code in memory, execute code, transfer data. That kind of stuff.
I would know that it requires block transfer to receive a PCM file from the PCM, and that most interfaces DO NOT SUPPORT this mode. So I would not rely on any commercial interfaces to perform this function. Maybe the newest B&B interface supports this mode, but I don't think any others do. None of the M-E interfaces do - I've talked to Paul Bowen about this specific function.
That's how I would go about it.
Anyone up to the task? Again, I don't have time to do it. I'm up to my ears in other stuff.
If anyone here is serious about building a flash by wire tool, this is essentially what you're facing.
Andrew