Hi,
I've never ever done this, so this reply doesn't form part of the substantive response I hope you will get. The subject fascinates me though, I notice a lot of traffic on this in photo.net, eg
http://photo.net/canon-eos-digital-camera-forum/00AGOo
I don't mean to be a distraction, so I am tip-toeing here, but I'd love to know
Cheers