You say that one drive is "in bad shape". I see no evidence of that. In fact you didn't tell us whether BIOS had detected it with its correct model number and capacity, in which case the drive would likely be OK.
In any case, I'm thinking that the best solution would be to replace the faulty chip. I say this because I don't know how the bridge IC spins up the drives. It could be that it implements staggered spinup, in which case it would spin up one drive, wait for it to become ready, and then spin up the second. In this way it could minimise the startup load on the AC adapter. This is only pure conjecture, though. Instead it could be that the adapter may be able to tolerate a short overload.
Anyway, you would still need to remove the IC switch in order to run wire links between its inputs and outputs. You may as well replace it. I would visit the Digikey or Mouser web sites and perform a parametric search on dual MOSFETs in 8-pin packages, one N-channel, the other P-channel.
For example, here are three parts that are used in other WD externals:
AO4616, Alpha & Omega Semiconductor, 30V Complementary MOSFET, N-Channel 30V 8A, P-Channel 30V 7A:
http://www.aosmd.com/pdfs/datasheet/AO4616.pdfAO4620, Alpha & Omega, Complementary Enhancement Mode FET, N-ch 30V 7.2A, P-ch -30V -5.3A:
http://www.aosmd.com/res/data_sheets/AO4620.pdfAO4619, Alpha & Omega, Complementary Enhancement Mode FET, N-ch 30V 7.4A, P-ch -30V -5.2A:
http://www.aosmd.com/res/data_sheets/AO4619.pdfhttp://aosmd.com/res/markings/AO4619.pdf (marking description)
I suggest you compare their specifications and pinouts against your APM4532 device. Perhaps one or more will be a suitable replacement. Let us know what you find.
Here are links to Digikey and others:
http://www.google.com/search?q=AO4616+O ... OR+digikey