Android :: Is There Way To Automatically Update Application?

I'm developing an application that will most likely be preinstalled on devices. It will be also available on Market. Is there a way to update those instances that are not downloaded through Market, since Market won't notify users about an update. I was thinking about, as suggested here, trying to contact my site periodically, and when update is available, download it. I'm wondering if there is a way to do this update automatically, so that user doesn't have to do anything (like running the package manually). Or, when my site shows update is available, to offer users an update through Market, even though it's not installed through Market. EDIT: This Market option would be preferable, because than users wouldn't have to check "allow install of non-Market sources".