If you can't manage that then the least you can do is put a link on each mobile page which redirects back to the desktop version of the site.
Some sites manage this very well (Tumblr just works, for instance).
Frankly, in this day and age your content and your layout should be entirely separate anyway and you should just be serving different CSS to me.
It is ridiculous that I should visit a link emailed to me by a friend, be shuffled over to the mobile site, save it to read later, and then be stuck reading the mobile site on my desktop with no easy way back.
Worst of all being YouTube, where mobile URLs don't even display the video if you view them on the desktop.
Please handle this better.
Original post on Dreamwidth - there are comments there.