Macbook clamshell mode - advice?

Thought I'd finally cracked (no pun intended) the issue of running the Macbook in clamshell mode. Plug everything into the various ports, making sure the monitor is switched on, hit the power button and close the lid: voila! When it starts then the external monitor gets the full feed from the booting computer, and it will run with the lid closed giving >5 hours battery life even with the wireless network activated.

Except.

Except when you leave it unattended for a couple of minutes and it turns the external display off to save power, as though it were the laptop display and hibernates. Then the external display will work briefly when the machine wakes up before going blank again (because the lid's shut) and it returns to the hibernation state. Then you have the choice of shutting down a restarting or leaving the lid open as you did before.

This is really sucky.

Every other laptop I ever touched in the last 8 years would automatically divert the video to an external display if one was attached when the lid was shut, saving battery power etc. After hibernation it would awaken just as it was before, using that display. Like the failure to handle some CDs and DVDs properly, I'm sure this is just a software issue.

Any other users out there have advice/settings suggestions (not that there's much that control panel will let me change anyway).

And one more question - anyone ever use a non-Apple power supply? It would be useful to have a spare, but at the £20 ebay price, rather than the £60 Apple UK price. However I'd prefer not to fry any batteries.