Finally, some answers had been answered to Windows Phone 7 community to bypass Marketplace to install App. ChevronWP7 is touted to be able to allow users to install app minus Marketplace.
According to the website, this is their first release and should expect some bugs. If you are brave enough, do try it. I tried to download it but my Norton 360 actually stopped the file as it has a suspected file (WS.Reputation.1) in it.
They have instructions on how to make it work and many mirror websites to download the file. Have fun with it.