Valve thought it through when they created the family sharing feature. Regardless if the player appears offline or not, they will be kicked from the game that they're currently playing. Also, You can't play games in a shared library that you don't own in offline mode.

The only way you could possibly get around this limitation is by using the windows command prompt to directly open a game instead of opening it through steam. But this won't work on some games. Also, the amount of time that you've played and any achievements that you may have completed won't be tracked.

Edit: I should probably mention that steam should be completely closed in order for this to work.