I have an idea (actually I registered here just on purpose to say it )
I now that Michael had some Thinkpads to test (W500? and T61p?) or am I wrong? And they have tp_smapi module which lets you to configure lots of things about your battery. For example if one does:
then the battery will discharge irrespectively whether the power cable is pluged in or not and the consumed power can be monitored as:
echo 1 > /sys/devices/platform/smapi/BAT0/force_discharge
The only drawback of this method is that the module is not in the mainline kernel, but building it together with the kernel every time (although, I do not think, that it might be 100% necessary) wouldn't very time consuming. And, overall, the bisecting could be easier, because one could write a simple script for that. And with Jimmy's suggestion to use
you could avoid the non-working kernel versions as well.
So guys, what do you think?