When your palms face the ground, the orientation of the two bones in your forearm compress the tendons slightly. So, I'd really like to try a vertical keyboard

When your palms face the ground, the orientation of the two bones in your forearm compress the tendons slightly. So, I'd really like to try a vertical keyboard. Kinesis makes them, but I'm not convinced I'd find the keys as comfortable as the aluminum Apple keyboards, which require very little pressure. What I'd really prefer is a makeshift vertical arrangement with two of the small Apple USB keyboards back to back. The trouble then is that modifier keys don't work correctly (like shift plus a letter on the opposite keyboard wouldn't capitalize.) Is anyone aware of a hack that could solve this?