I inserted the line
hwif->serialized = 1;
into "static void init_hwif_data" in driver/block/ide.c

I'm a bit short of time at the moment, I'll take a better look later.

As far as i can tell the master/slave communications are done over the pdiag and dasp signals and that these signals are not used by the host, if that is the case then there traces can simply be cut by the header on the CF adapter, to isolate the two master/slave pairs.

R.