I think they could have a generic image and the "paid" stuff could be installed later from the store after some sort of activation/license code entry/whatever. I think it could more or less work out of the box (minus the activation bits) as it's already possible to install Android & Exchange support from the store.

BTW why you don't want different per-user images:

• you need to store or generate sizeable per user image vs just storing a single generic image per device
• harder to verify you image is not corrupt or maliciously modified, as you would need to provide & check checksums per user
• all the privacy implications of tying personal details and device information together by the per-user image